Helpless

in 2007 i app**** for a cellphone contract from x-cell communications, i lost my phone 3 months later and never got a replacement because it wasnt insured,i continued paying until i lost my job. when i got another job i called them and enquired about my balance and they said it accumulated interest,i didnt know that celllphone contract can accumulate interest ,i didnt even do a sim swap after losing the phone, i just wanted it to go away.i lost my job again and thus stopped paying and in the beginning of 2015 i received a call from kasimira trading saying that they took over from x-cell so now i owe them money,i made an arrangement with them and started paying them without a phone or a sim card, today on the 24-03-2016 i called and asked about my balance and they said i still owe them R4006.17, all the debit orders that went through add up to R6965.00 so its more than R11000,00 for aan E250 samsung phone , I FEEL HELPLESS , PLS HELP