Interest charged twice

Interest charged twice on my Foschini group account *** on my July statement interest was added on my outstanding balance and also taken from my available credit and i feel it not acceptable i spoke to Janine on the 18/07/2019 she advise to me that they only charge it on my outstanding balance,i requested to speak to her manager waiting on the line for more than 20minutes i dropped the call.I phoned on the 19/07/2019 spoke to the Manager Shereen advised that they took it from my available credit how come because i know interest can only be charge on your outstanding balance i want this thing to be sorted out am very unhappy with they service Foschini is pathetic am going to pay of this account and closed it i don't want anything to do with Foschini group.

Kind regards Chereese