Mango taking over 5 months to pay a refund

<p><span style="color: #333333; font-family: Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif; font-size: 13px; background-color: #fafafa;">I had double booked a ticket with Mango, due to their site hanging/timing out and then not receiving confirmation of a flight I booked, I then re-booked a flight and was charged twice. I informed them before my flight was to take off, and they agreed to refund my ticket. This was now nearly 6 months ago, and with roughly 40-50 emails I have sent following up every 3-5 day asking when this can happen. They paid a refund to a debit card number, which I then checked, and did not receive funds, I then got a letter from my bank, confirming the funds were never paid to my account, as well as that Mango - cannot pay directly to a debit card number as this will always fail, they will need to pay to a bank account number, linked to the debit card I used to book the flight. Now they are going up and down, saying they will speak to their finance department, despite the proof I have given them I cannot get a response or re-payment out of them. They are simply saying, they have paid. That's it. They only refund paying to credit cards. I cannot believe that I am the first person to experience this, since my bank was quite adamant that there is no way a payment directly to a debit card will clear. So now what do I do? I am tired of following up with no action. Worst service ever experienced and I surely wont fly with them again, and urge everyone to stay away.</span></p>