Upgrade nightmare

I have been trying to get my contract upgraded for a month now. Keep getting sms's from MTN my upgrade is due , if I go to a store they say only in September but my last upgrade was 06/2021. Nobody has been able to tell me why or sort this out. I must've made 20 calls already, nobody understands why and promises to sort it out and get back to me but I never get any follow up. Beyond frustrated as their service agents seems unable to find the reason. Very poor client service!