Bad service after contract cancelation

I requested a contract cancelation for the Acc A*** cellphone number *** on the 28th April 2020 and it was changed to Prepaid on 05-05-2020. The problem now is I cannot receive calls at all since the 5th of May 2020, I called 135 they told me to do simswap because there are no call barring, I went to MTN shop they told me it is blocked by retentions and they cannot perform simswap, they gave me this ref number: ***. What's so disgusting about this I can make out going calls, sms and receive sms

Please kindly assist with this issue and I am kindly disappointed as I am still having existing account with MTN, it has been a remarkable 3 days without receiving any calls.