Toyota financial services poor excuse for not refunding clients money

My account was settled with Toyota Financial services, and they still took off an April installement. I then called and asked for a refund on the April installment only to be told, sorry we have a backlog we don't know when you'll get your money back. What ludicrous kind of answer is this. Happy to be paid the settlement and the the installment on time, but when asked to refund money which is not theirs suddenly there's a backlog.