They never gave me my promised refund

Have been very happy with booking.com untill I needed a refund! I was granted a free refund even though I had already paid in full. But more than 26 days after the claim to have processed the refund, there is still no sign of the money & they refuse to send even the most tentative forms of proof of payment! They expect me to take it on face value that a reasonably large sum was returned to me, even though there is absolutely no evidence that it was. I hope they have been paying the wonderful properties I've stayed at more timeously!