Poor service from cancelations

I contacted vodacom cancellations in March/April 2021 to cancel 2 of my contracts for Pre-paid. Today(6/10/2021) saying i am in Arreas! After numerous times i managed to get thru and was told that nothing can be done as my account is blocked on their side. From those 2 contracts 1 was switched to prepaid and 1 didnt. How am i responsible for this error made by vodacom? I need assistance before they suspend my line for their error! Its 2021 and vodacom cannot be making simple errors!