Bad service

Cell c called me March 2021 to offer me a router because I did app**** 2years , and they said is R300 sim card with router and I agree yo that on the 16March they debit R411 and I was surprise was they debit more because I was expecting them to debit pro-rata. My debit order date is on the 7th of every month, on 7April 2021 they did debit because they did debit now I receive a statement that is showing me my outstanding of R124 and am no longer paying R300 a month for the router accounding to them my router is more R500 and I didn't agree to that what I know is am paying R300 a month I don't know what is happening and I did call them but I didn't get help about that . The person who called me is Event from cell c to offer me the router, when I call him he doesn't know anything even the day they debit R411 from my account I did tell him and he said the will call me .am not paying for something that we didn't agree on R500 is too much for me just for router