Possible sender fault

ok guys, was jacking car up from the diff, slipped off the jack and came down on the jack on the fuel tank. Didn't really damage the tank at all, just a bit of a dint as the jack is a decent size.

I noticed my fuel tank now reads full. I disconnect the feed wire from the sender (I only have one wire, some have 2 wires, like an earth, mine has one), and it still reads full, I earth out the wire, it reads empty but very very slowly creeps towards full.

Any ideas what my issue could be?

Thanks in advance.