MTN Grey list my number

I changed my banking details a few months ago. I updated my banking details on both my contract. One of my contract accounts debit order went off with no problem but my other mtn contract they kept trying to debit my old bank account. I emailed and phone to fix the problem. I still paid the outstanding amounts every month. I again phoned to confirm my banking details details was correctly updated after my last call to mtn but it still did not go off. I decide to go onto the mtn app and check all my details, i found that my default cellphone number was changed. I correct the number. Now i found MTN put my number on a grey list and im unable to use my number which i never missed a payment on for more then 20 year. I doubt i will continue with my contract next year when it ends.