Theres a night in Glasgow called Sub Club, Im not aware of Subdub ever kicking off about that.
Theres a night in Wrexham called Freak, I know there are several others with the same name
Theres a night in Liverpool called Superfly, I know of at least one more UK night called Superfly
I promote a ...

Surely thats two different locations and two different spellings though?

What he said.
Even if you'd copyrighted the name Rubberdub and they were in Nottingham you wouldnt have a leg to stand on with getting them to change the name due to the different spellings.

Just accept the fact that ...