THEY DONT WANT TO GIVE US A STATEMENT

My mother took out a contract phone for me in 2012 but didn't pay it well so they handed it over to the lawyers (MBD) then i took over by paying the agreed amount and sometimes I payed more until last week when I called the lawyers to request a transaction statement to see how far I am with the account and they sent a settlement letter that showed a big amount so I called them to ask where are they getting this amount and I requested a statement not a settlement letter. Then after a day they called my mom and told her that she must stop paying because her account is fully paid. So my question is why now they only telling us we finished paying but the letter shows a big amount? so I got angry and went to MTN in Lynn wood to get answers but that didn't work out because the lady who was assisting me had to call her head office and they kept on transferring her to different departments, one finally said the account belongs to someone else and not my mom ( WHAATTT) so does that mean I was paying for someone else? Is that reason why they cant give us a statement? I am not happy with MTN. people are complaining about it and know I know WHY.