I need my number back

I have tried everything to get my mobile number back from Cell C which they deregistered after cancelling my contract but to no success. I now can't login to my social media accounts since my number was the only way I received an OTP. All I need is my number back so I can port to other networks that treats people better. Cell C promised to get this fixed each time I write a review but it's only a PR stunt, they haven't taken any action or bothered to get this resolved.