Cancelling my sim card and number!!

I have had my MTN number for more than ten years now and about two years back I took up the offer to get top up airtime from one to one. I cancelled the contract on the 19th of February and they said that it would be effected on the 19th of March. On the 24th of March, my number was canceled without any warning. I called MTN and they said that the number was cancelled by one to one. I am very upset with one to one because, this was MY number that I had before joining their contract , they had NO right to cancel my number as it was not their number to begin with! They have seriously inconvenienced me and I am busy running around trying to get my number reactivated.