MTN giving wrong information to credit bureau

I found out that I have a missed payment from MTN on my credit report I contacted the credit bureau who said MTN must send them an instruction to fix the error I tried calling and going to the physical store but everyone keeps saying I must contact the main office I finally found an email address in May and I have been sending emails back and forth with no help Every time it's a different person replying and they don't seem to care I was told that the matter is being investigated in June and now in September still nothing I'm really disappointed in the level of poor service that I am receiving My credit score is affected by this non existent missed payment and MTN has the nerve to send an email saying I'm due for an update