MTN gave my contract number to someone and "cant give it back"

My number was migrated to a pre-paid and given to a new person. I was still on contract with monthly invoices. I went to MTN and they said they cant help me to get my number back. They broke contract and just gave my number away. All my bank accounts are linked to this number, work clients. I will not go back to MTN ever in my life. They just brake contract and leave you stranded.