Bad service

I have existing loan that i have paid an amount on meaning the following debt order means the loan will be paid in full, unfortunately they still deducted 2 x instalments afterwards which results in them owing me money. Tried multiple times calling them and sending them emails with proof of payment, no result as yet or even anyone from their side contacting me. Phone calls are put on hold for 15min plus and then call gets dropped. They are quick the give loans but to settle and resolve problems they are very poor.