Shocking service

I have been begging these people for 3 months for a refund of a premium, which I paid manually. I forgot somehow that I had authorised a debit order for this and made a manual payment. I have email numerous people and their "go to" response is always that I must send the proof of payment, which I have now done more times than I can remember. Every month they "religiously" take a debit order from my bank account despite the fact that I have overpaid them. Their account's department are clueless