Harrasment - I was not happy with the services which was informed and i intended to discontinue

Hello,
This is just another case where a big organisation trying to us to give in into their harassment.
I have been using the said card for a very long time, more than 6 years, where there was no issues till last few months (since jan17). I was not happy with the services which was informed and i intended to discontinue with card in apr17. I made a request which they said will look into the services and let me continue. This happened twice. Third time in jun17, i placed request for the same when i was told that i had more than 2400+ POINTS EARNED OVER THE YEARS will be forfeited. I told them to adjust the same in final payment which they refused. They also told me that i can redeem them first and then discontinue it. I was promised that i will be sent 2000 rupees voucher of Titan in Jun17(as it was in multiple of 500 so 500*4). I waited for more than 3 months with repeated request for vouchers but to no avail. I had a limit of 96000 out of which only 7000 appx was used and conveyed that i will clear amount as soon as i receive my vouchers.
Once i stopped payment and made complaints as it was more than 3 months since they have been trying me to continue and not talk about my concern, they blocked my card without resolving issue and i was told that HARD EARNED POINTS over the years have been forfeited by them and i was bombarded with calls from collection department. I made a complaint(s) to customer care but no solution, Once i made a complaint and i got a call which i was not able to pick, without any effort or try, i received a mail that the complaint has been closed as they could not get in touch with me.
Despite being a customer with SBI for so many years, where over the years i was offered many advantages like offers and INCREASE IN MY LIMIT (all an happen with track record only), i never availed any as the limit was enough for me. When i faced issues i was told that i was a valuable customer and should continue.
This thing was not taken up at their end and was completely ignored and only thing after 2 months, i was made defaulter for the nominal payment. i was bombarded with collection dept calls, where they were not ready to forward my grieve to concerned department.
This interaction is not about vouchers its about how i was harassed for payment and was totally ignored, despite their promises. It is always not the customer at fault.
FEW FACTS
**I had much more balance in my account than my outstanding at any given point of time.
**My limit was 96000 whereas i used only 7000(at time of dispute) shows that never wanted to cheat.
**Was offered 300000 limit. That can only happen if you have a good track.
** Never defaulted in loans and other credit cards i possess.
These above clearly suggest my intentions, yet they are harassing me with unlimited number of calls for collection dept. They also don’t forward my reply to concerned dept. but only ask for payment. They also say that they have forfeited my promised earned points as per T&C.
I made the due payment which i had utilized after deducting appx 2400.(my points value)
Now they keep sending bills with interest and late payment charges and no solution.
Please help