Cell C Contract Cancellation

I’ve had the worst experience with Cell C.

Took out a contract with them which started in May 2019. Everything was good until the contract was supposed to be cancelled in May 2021. Now I’m getting calls that the contract was only cancelled in July and that I need to pay for June and July too even thought I went to their Boulders branch in March/April to request for a cancellation as my Cell C sim suddenly stopped worki sometime in Feb/March(something which I communicated to Cell C)it’s not fair that I’m being forced to pay an amount I know nothing off especially because the sim has been inactive since Feb. Why were they still loading data on an inactive number? They are now bullying and threatening me with lawyers and that I will be blacklisted.