increasing balance

i have been paying this account from last year since. but from august i have made recurring payments and still the account is not going down. from august 2014 the account was owing R5838.88 and now its sitting on R3786.71. however payment has been made every month. i have paid the account the correct instalment and sometimes i paid more but still there is absolutely no change. i am also not getting correct statement. they are either late or don't come at all. i have tried speaking to the call centre agents but no one is helping me understand my frustrations. just last in april i paid twice on the 4th april i paid R500 and the balance was R3813.66 then on the 28th april i paid R500 and balance was R3573.54 then on the 27 May i get an sms with the balance of R3786.71. it doesnt make sense!!