Hello Guys,
Let me share what my call history was like before I started taking the steps which I'll be sharing.
Used to get 10 to 15 calls on each of my number, yes my DND was fully active. These were mostly from finance companies, stock market channels, credit card sellers, donations. I was tired of telling them that "I have surrendered your credit card, I no longer want to enroll in it again", "My number is on DND list, please check before calling me", "I do not need a personal/pre-approved loan". I got a scripted reply, "We will update it in our system & ensure you do not get a call next time" which we all know never happens

. Don't want to take any names, we all know the infamous callers.
As of now I get a maximum of 2 to 3 calls which can be handled easily on worst days & some sunny days days I get 0 calls from telemarketers.
I'm not talking about changing numbers, its extremely painful to switch your number, have it updated with banks, friends, demat account, insurance, mutual funds, electricity dept., and god knows how many places which is a herculean task. I'm talking about reducing the spam on your existing number without having to pay any additional fees.
I use an Android phone, I am not sure for the steps/apps in an Iphone apologies in advance to Apple users if this doesn't work out for you.
1. I have installed Truecaller, it does have a data privacy concern highlighted multiple times, I haven't found any good alternative yet so I'm using it. You may skip this step, however your results may vary & you may need more manual intervention. I've pre-blocked all numbers starting from +140 to win half of the battle,
In Truecaller App go to settings > Block > Block Someone Manually > Number Series
Over here enter "Number that starts with" "
+140",
+9140
The feature to automatically block 140 series is currently a premium feature, however we can manually enter the series to have it blocked to avoid paying the premium.
2. Enable Truecaller Caller ID (I haven't set Truecaller as my default dialer), this will ensure the spam callers are tagged in red, so you know if you've to pick it up and report to proper authorities (next step) or let it ring.
3. Going 1 step further & making their life miserable to ensure they don't bug you or anyone else
In Playstore there's an app called "TRAI DND 3.0 (Do not Disturb)" published by "Telecom Regulatory Authority of India (TRAI)", install that app. I accidentally stumbled across it, read the reviews & thought to give it a try.
Register your mobile number(s) with it. The app does require you to re-register everytime there's an update, remember to do it.
Now everytime you receive a call from a telemarketer, & if you answer it, you can report it as telemarketing call through the Trai App. Open the app & tap on "Report Voice UCC", fill in the necessary details & submit. There's an option to report SMS as well, haven't tried it yet.
What this does is puts the telecom provider in action & investigating mode. Once you complain, you get an acknowledgement number via SMS (I use Airtel & Vi in the same device, so while complaining be careful to report it to the correct operator, Ex. received a call on Vi but wrongly reported it to Airtel won't work). You get a tentative date by when the case will be closed, I do not keep a track of every case I report but ensure to religiously report every telemarketing call I've picked up without fail. There is an option to report the number to Google, but that would mean "Don't bug me, but bug others", however reporting through the Trai app would mean "Don't bug me or anyone else" as the operator is forced to take action on something which is backed my Trai, whereas operator may say "Meh" to a google backed complaint.
Ensure you complain within 3 days of receiving the call, if you do it after 3 days no action will be taken, you'll get an SMS stating "Sorry bud you're late on this one, nothing we can do"
Here are some screenshots of the updates I've received from the telecom operators,
I can recall mostly 3 actions in these texts,
1. 1st time violation, warning given & put on 1 month usage cap.
2. 2nd time violation, put on usage cap of 6 months
3. Number disconnected
The usage cap itself is a good deterrent to stop calling from that number.
After having reported these calls to TRAI App for approximately 2 months the volume of these junk calls has dropped significantly (From 10-15 a day to 0-2/3 a day). Many will say, these guys can obtain new connection(s) and start to bug you from the new number, the thing I've observed and read in the app reviews is, once you start reporting you get some sort of VIP tag (Made up word, but you know what I mean) as in "This nuber is not to be messed with", you don't get bugged by these guys, be it an old number or a new number, the key is to report them.
It'll be unrealistic to assume you'll lead a spam free life, not possible as some or other guy will end up calling you to stick their product, best you can do is minimize that window which allows people to reach you.
Enough gyan, screenshots below. (Screenshots are a bit old as I barely receive any spam calls now, there was just 1 thread of Airtel, many reports done) I'll share future updates on complaints as and when I receive any updates.
I hope this post helps you lead a spam free life.