Not reducing my balance every month when I pay

I have been paying my account from December instead on the amount going down it increases. I asked in December and we called yhe help desk they said it was cause I was on a 12 months plan which I asked to be removed and put to a 6 months. In January I paid R2000 and the balance came back still as R6288. They said it will show in February . I paid last week Friday 8March balance was instead R6382 after I paid. I even have receipt to prove that this people think am stupid. Am supposed to finish paying in april I dont see that happening. Be warned