Mweb failing to inform me about outstanding balance when canceling and putting a high service charge

Mwebs customer portal is a nightmare. I had issues logging in as my old number was no longer in use due to my phone being ******. I was unable to pay 2 months and as a result my services was suspended. When I finally manged to get through to a consultant they sent me an email to send proof of payment. I did so and my services was reactivated. I then contacted them to cancel it. The consultant said no problem and never informed/made me aware of any outstanding balance. I did not see any invoices as the old email was not in use either due to not being able to log into it.

I now get I vices from their debt collector who put R500 service fee on top of it. I have tried to get mweb to send me a copy of the email where I sent proof of payment as I am convinced that the last payment might have no reflected or if it did why was I not informed about my outstanding balance when canceling the contract. This is purely Mwebs fault. If I do owe I am more than happy to make arrnagmenets to pay it but I refuse to pay the service fee of R500 to a very unprofessional debt collector who calls and accuse me of being a late/bad payer