Still no response 2 months later!

I am at my wits' end. Telkom bills me for a phone that Used for a week, it was 349pm . I paid the initial 349 and used the phone and returned it as it was not according to my specifications. I still get invoiced and debited and i normally reverse the debit order. This month the debit order went through as \NUDebt "and i could not reverse it. for R689.70. of which i still don't know what its for as i had paid the 349. PayingR1047 for a phone i used for a week is ridiculous and i demand answers. This is probably the 5th complaint i have written"