Cellc acc balance but still in arrears of of a sudden

My cellc cellphone account was in arrearsof R469.45 in february,on the 8th of february 2021 i paid up the amound ans sent emails to cell collections to be sent a paidup letter,but my emails were not responded to,today i just received an sms stating my acc is in arrears of R900 something,i want to know where that amount comes fromm becaused i paid up my acc and the balance was R0.00 in feb after i paid,i want cell c to clear this nonses.