MTN cellphone insurance underwritten by Guardrisk.

I upgraded my MTN cellphone contract in November 2019. I cancelled my insurance cover for my old phone within the same month but for some reason my account was debited at the end of December and nobody can account for this. I’ve been sent from pillar to post between the contract division and the insurance division, the insurance fee is still included in the invoice for the end of January however I cancelled the service. Nobody is taking responsibility. I’m appalled.