MTN gave my number to another user

I'm very dissapointed with MTN. They have given my number that I've been using for a long time to another user. The number is *** and this person answers my calls and send messages to people on my contacts pretending to be me, he's even asking for money using this number and people think it's me because they still have this number as my whatsapp contact. Can MTN deactivate this number instead of giving to another user because the person using it is doing ********** stuff.