Worst nightmare

6 years ago I bought mtn simcard n port it to cellc after 2 years now last month I found out mtn port back my number to mtn.. My number is registered to my banks, insurance everything.. When I ask why they port it back to mtn customer care doesn't hVe answer they said it happen automatically now I ask for my number back they say must do simswop on progress was told the is nothing on a number like last recharge an staff, they told me must go to police station to make affidavits n send to them to claim my number.. Who's fault was it to port my number back to mtn from cellc I must use my money to go to town at police station to get affidavits for what. I want my number back asap