Refund not processed

I purchased beds from Lewis on account on the 27th July 2020. And on the 18th of August I settled my account in full so the account was suppose to be closed. On the 27th August Lewis still deducted the installment on an already settled account. It's been over a week after I phoned them, ref 689342,to rectify it but still I have not received my money back. It's so frustrating because if it was me not paying my account then they would have been on my case 24/7.