Customer waits three weeks for a trace of £500 sent to a closed account

Sent £500 to a closed bank account 3 weeks ago - money still missing. What should I do? I accidentally transferred £500 from my Revolut account to my sibling’s NatWest account, only to discover afterwards that they had already closed that NatWest account. I contacted Revolut straight away. They said they would raise an enquiry with NatWest to trace/recover the funds. It’s now been about three weeks and I haven’t had any meaningful update. The £500 has left my account, but it hasn’t been returned and obviously never reached my sibling. Has anyone been through this before? Is it normal for this to take this long? Should I be chasing Revolut, NatWest, or both? If the destination account was closed before the transfer, where does the money actually go? Is there anything else I should be doing to get this resolved?