I had the opposite problem. They closed my account with very short notice back when they decided to purge all customers with any connection to Ukraine. This was an account for a US company owned by me a US citizen receiving payments from the US and paying contractors in Hungary, but once upon a time I had paid contractors in Ukraine. All addresses and legal agreements were in the US.

So if anyone else is having trouble closing your Mercury account I suggest you contact support and ask to change your principal location to somewhere in Ukraine. Your account will be closed in no time.