Keeping same number with new contract

I'm an MTN customer for almost 20 years and had good experiences in the past until this year. Just before the lockdown started I upgraded online with a rewardsco company and wanted to keep my old number as I use it for my business. They told me I need not cancel my old contract, it will be done automatically. Two months later I realized that I'm paying for two contracts by debit order. I phoned customer services numeral times, was put through to different people as I didn't just want to cancel the old contract, I need to keep my old number on my new contract. I'm happy with the new phone and contract, I just need my old number. I phoned the MTN offices in Johannesburg a few times, but they just told me there is nothing that they could do. I did not want to except it and phoned customer services. For weeks on end I tried different people at the retentions section at customer services to solve the problem, often waiting for more than half an hour on the telephone before someone responded, also being cut off many times! In the end I was told that they'll send an email to the rewardsco company to rectify it. Someone at the company did phone me and told me there will be an investigation and they will come back to me within 3-5 days with the outcome. It is now 2 weeks later and nobody contacted me yet! I do not want to pay for 2 contracts next month again and can't cancel as I need to use my old number. I am really very disappointed with MNT and expected better service for a loyal customer after all these years! I really won't be able to recommend them to anybody else. If there is anybody who could help me with this ongoing problem, please advise!