Bad customer service

Goodday

My name is Miss Bulelwa Chiliza in 2017 I bought a fridge at Morkels on credit account no. *** I have been paying for this account via debt order and this month end of August, I would have been paying off this account however last months installment was not debited from my bank account the money is debited every last day of the month however last month I was not debited, today I received an sms and a letter of demand from them informing me that the account has been handed over to F and D collections which has a cellphone number as they contact number which makes it even more unsafe and not trustworthy of me to enquire information on this account from them because when I called them they asked for my ID number as I hang up the all within they no. *** and called they collections department on *** I spoke to Tebogo Mlaba who could not assist me who then referred me to her Manager Foster who was also rude and hang up the call on me my query with them was since the money was not debited last month they will be interest charged on my name for an account that was supposed to be paid for and debited by them. HELOPETER please help.