QUICK TO DEBIT... FAILURE TO REFUND!!!

Worse service ever. Been waiting for a refund since 28 March. Bank confirmation letter sent 28 March, 4 April they send me a debit order mandate. i question this because why are you wanting me to sign a debit order form for a refund? no response, just a 1 liner saying refund requested, allow 5-7 days. 11 April i follow up and now they did not process the refund because there is no bank detail which they've had for 2 weeks!