Same problem since October 2022

I upgraded my contact in October of 2022 after that I couldn’t purchase data using the short code *136#. This means that when my data is finished for the month I can’t top up. I’ve been calling for assistance since October 2022 with no solution. Almost 6 months later I have reference numbers: Req *** SMC *** SMC *** to fill the bible but my issue can’t be solved. I’ve been told to to manually search my network, reboot, remove SIM card there is nothing I haven’t tried and I still have the same problem. I’m stuck with a contract I’m really not happy with. Is it possible to cancel my contract because a small issue can’t be solved. MTN I’m really not happy.