i received £9000 and now they are claiming i didnt sell them an item and it is in dispute

[GeorgeHeaps]

please help! 

i got sent £9000 out of the blue and now it is in a 'dispute' saying i couldn't sell a bunch of drones.

However i don't sell drones and especially for £9000, if i refund will i lose any money or will it simply be sorted and they get the money back with me not losing any money

thanks so much if you can help