I really don't how this works for the scammers but what would I do if a large amount of money came into my account and I then received a phone call to asked for it back my answer would be as follows " meet me at my bank at 9-30 Monday morning and we can go in together to sort this out.
About 1 year ago £1,000 was paid into my business account from a person who's name was not on my customers list?
3 days later I went into my bank to inquire about it and telling them that no one owes my £1,000
The bank advised me to just leave it there and see what happens, to this day a year later no one has claimed it and besides I've spent it now LOL