Confusion from accounts department leads to a heavier burden on a loyal customer

I wish to make a complaint against Edgars. I am a terribly unhappy and frustrated customer. This all started in August when I made my last payment. When I made a payment to my account of R70 I received a receipt stating that the amount still outstanding was -38.44 . This error of whatever it was caused major confusion as I thought my account was settled however after being emailed by the Edgar's account department I see that this was not the case. Now I have to pay interest so to speak for the confusion of what I feel the accounts has caused. This experience leaves a bitter taste in my mouth as in this struggling economy it is certainly becoming hard for loyal customers such as myself to have accounts. Also I had asked the accounts department to change my address but again incompetence prevails...I am certainly going to be more frugal now as I do not see why loyal customers such as myself are penalised for the backlog of all the dishonest ones...