MTN has no fail safe if your number is hacked

My mtn cell number was hacked aswell as my watsapp. The person that hacked it was asking all my contacts for money via ewallet. I contacted mtn to block the number and they said they can't do it and that the number needs to be inactive for a month. So basically if your number gets hacked there is nothing they can do. It suprises me that in today's world with all the new technology that they can't simply block a number that's been hacked.