Unsolicited sales calls. They always start with silence. They don’t tell you what company they are calling from. If you try ringing back to see if they legitimate, you just get a recorded message at best.
I checked up one company that keeps calling, they even give different names. Companies House often show the company as dormant or having been struck off. A lot of them seem to be based in Birmingham.
It occurs to me that frankly that the banks themselves should be automatically refunding this money if they are in error, but with the present bunch of cunts in government that’s not going to happen is it.