MTN migrate number to Vodacom and the revokes it

I had a contract at MTN (Hartbee****rt) for more than 5 years at least. It was my wife Cellno *** which I then decided to cancel about a year ago and took out a new contract at Vodacom (Hartbee****rt). The only reason was because in our area Vodacom reception was better than MTN. I canceled the contract and did a sim migration to Vodacom. Everything was working 100% for the first year, meaning my wife got calls direct calls and WhatsApp calls. I would take as a sure thing that the migration from MTN to Vocacom is all in order.

For the last 6 months just suddenly my wife could not get any direct calls to her number and could only be called via Whatsapp. We went to Vodacom (Hartbee****rt) and then said we needed a new sim, which we did and waited 24 hours, and would then work. But it did not and since that, this matter could not be solved.

My wife went to Vodacom in Pretoria and asked for help there - They investigated and found that the MTN migration which according to me was done, was now not done

My wife went to MTN (Hartbee****rt) and was informed they allocated this number to another client at MTN.

How can this be if, for the first 1 year, everything works 100%? We asked MTN to correct their mistake and told my wife it was not possible. Now we have my wife with a Vodacom sim getting WhatsApp calls, but not direct calls which is at MTN.

I would like MTN to correct their mistake.