Unknown debit order from dstv

I have an agreement with dstv multichoice for a debit of R405 a month for a compact subscription.. Last month i couldn't pay hence they cut off my line of which i understand. My problem is that they now came back and tried to debit R137 of which i dont know where it came from, now fnb has charged me R100 for an unsuccessful debit... Actually where does this R137 come from? I dont have an agreement of that amount with them