Unsatisfactory service

I've been with rain for the longest time, I've never missed any payment. It happened that my two Sim cards that came with the router 1 got damaged and the other got ****** which I reported the matter. Soon after that received email that I wanted to upgrade the Sim cards to 5G which I've never did, called them which they promised to fix now my subscription is not what I signed up for it's 1000 not the 625 that we initially agreed upon. The first time on July my acc was 700 something and August 1000 which I paid when I asked again about this they told me that I wanted an upgrade then said if you received such email from me why haven't I received a call from 1 of your agent to confirm with me. Then the agent I spoke to said he was going to open a ***** case. I still have the same issue till date. Now they want me to pay 1000 that I don't know what it for which I'm not going to pay I've been paying 625 without any delay now they demanded me to pay for the money outstanding amount...