Number just taken back

So i had a number for years, and didn't use it for a while and MTN just decides to throw the number back into the pool. I think this is very unfair as i am struggling for quite some time now to retrieve this exact number. I need this number for work purposes as it is linked to most of my stuff and everyone knows that number. I have messaged MTN via Twitter and made numerous phone calls but to no avail, and the longer i leave it the harder it would be to resolve this matter.