Account changed without notification

I am paying my wife's account ***---ID: *** regularly from day basically the very same day when I received her statement via email(we are sharing the same email). As is practice when one is using EFT and always paying the same recipient, you programmed the required bank details and one that is done to just click on your "saved recipients" and do the payment. I have discovered now that CELL C has changed their Nedbank account WITHOUR NOTIFICATION on Statement 04.05.2021. For 6 months Cell C has accepted our payment on this so called wrong account no *** but then advise me that they did nor received our last payment i.e. R349.89 dated 8 November---I even sent an email to them with proof of payment---NO RESPONSE. They have again sent us the statement yesterday and then I phoned them to request why they did nor received our payment---IT WAS THEN THAT I WAS TOLD THAT THE NEDBANK ACCOUNT SHOULD BE ***. I duly changed the details on my Nedbank account (saved recipients). I expect CELL C to rectify the problem to request Nedbank to transfer our payment of 8 November from to old account to the new account--and update my wife's records accordingly. Question: Why did Cell C accepted 6 payments (6 months) but not number 7 on the same account? How did they handled and accepted the payments realizing that we use the old(wrong) account number? I challenged them to show us when they advised my wife re the change---or they could phone as well----bad management/service on this issue from Cell C. I will not pay the R349.89 again except if they credited MY Nedbank account with this amount after which I will settled the account via EFT on the "new" number. For the record we have paid the current new statement amount yesterday 6 Dec INTO NOW THE CORRECT NEDBANK ACCOUNT