MTS / Sistema Shyam TeleServices [SSTL] — mts postpaid bills

I was using mts dongle in 2016. When i took the dongle the plan was 550pm and my plan details were as follows.

Your mts data card number : [protected]
Your account number : [protected]
Your tariff plan : revb-550-5gb day_5gb night-unlimited
Monthly rental : rs. 550.00

Despite of being in a prime location in city where your executive tested and showed me that the signal strength is high, i never got browsing speed more than 100kbps, forget downloading, it never worked.

On 5/9/2016, i called mts customer care and informed that my dongle is broken, i would like to have either a replacement or a new one at subsidized rate. They informed me to pay off the remaining amount and then the issue will be taken care of.
The payment portal sucks. It never process payments. On 6/9 i wrote to customer care informing the failing payment attempts with proper screenshots. On same day i wrote mail about broken dongle as well.

Several times i spoke to cc to close my a/c.
No response, no follow up. Worst service ever.

Then all of a sudden i receive next bill claiming my bill amount to be 1300+. Claiming money for unused month as well.

I started receiving hell lot of death threat kind of calls from your customer care and one lady put up an offer saying there is a 50% waiver on the outstanding amount, if i pay 630 that is enough and the account will be closed. So i paid it sick n tired of the constant harassment.
I have the receipt.

Right after their offer for settlement they again started calling for remaining 630. Now am getting mails saying i have to pay 734.

For what?

For not delivering promised speed?
For not responding to my cust care queries?
For harassing me day and night on calls?

I have all the data from beginning, including screenshots of your pathetic speed below 100kbps while am subscribed to high speed band that too on beginning dates of 5 different months.

I have all the written conversations in my mail. I can attach the screenshot if needed