MTN is intentionally *****ing me R1855/ month

In December 2025 I bought a phone and a wrong one was delivered, I returned it back and delivered at an MTN shop, they gave me RTS number and I called to officially cancel the contract. Contract was cancelled or at least that is what I was told. In checking my invoice I found that I have since been paying for this phone. I have tried several calls with cancellation team on 135 but they are dropping the call. This contract is R1855/month . MTN has literally committed *****.