Contract not closed

I am sibusiso mangwane, i renewed my contract after the previous contract ended and I called them to close the account but instead they didn’t and it continued to accumulate as a monthly a subscription in which I don’t even know about or even use. I was paying R100 monthly and I upgraded to a R200 monthly contract. Now I am being told I owe R1300.

Please help me fix this issue because it’s not my fault that they didn’t close the previous contract