Edgars - Dishonest Interest charges on interest free account

I've been a loyal Edgars customer for over a decade, but lately, I've been charged interest on my 6-month interest-free account. Numerous emails have been sent to get the ******** interest reversed and Edgars/RCS/Edcon fails to respond regardless of the queries and requests to rectify the account. Can anyone assist in getting this resolved? Even at the store nobody seems to be able to give me a straight answer or solution. Is this a common **************** tactic?