Need my cell number back asap

Mtn, why is my no. deactivated and given to somebody else. I last used my phone to make a call in March. It's unfair. I was unaware of th rules of deactivation. I had only ported from a contract. My no. Is imp. It's linked to my banking etc. I had used my phone every month in regards to smses etc. It's very unfair to do this. Please I need my no. back in any way possible. Kindly reactivate my sim and surely you can give the new subscriber a new no. As it was just activated today perhaps. As today is only 91 days since I made a chargeable call. Surely you can explain to them. I am a loyal customer and surely it is possible for you to help me. It's my no. That's linked to important stuff and not the new subscriber. Please.