Cell C committing ***** by extending/ changing contract without customer agreement

I phoned 084 143 and went through to the cancellation department, only to be put through to the "collections" department. I did request a direct number, but was told I can only be transferred. As per usual with dealing with Cell C when you have a query to sort out, I was left on hold because of "high call volumes" and advised to email this account. I cancelled my account on 01/09/2021, and when I was sent another account statement, reiterating that this account has been cancelled in an email (20/12/2021) sent to *** as I was advised (again by an electronic voice as Cell C does not answer its phones). As far as I was concerned this matter was now settled. Imagine my surprise when I received an email from a collection agency saying I owe Cell C money. Please note that this is for a Fibre account, which was on a month-to-month basis, with a clawback on the installation over a two year period. The contract started on 07/08/2018 and was cancelled 3 YEARS later on 01/09/2021. Note that we were still paying month-to-month so the question of time periods being extended never arose, as this service can be cancelled at ANY time after the initial 2 years and clawback. I.e. we do not need to actually cancel anything, we simply stop paying for the service and it is automatically cancelled. This was confirmed by your sales consultant when this contract started. No communication was sent to us adjusting the terms of this agreement.