Update:
Took off the display, switch and throttle to post back with the battery and charger after talking to e-bikes direct this morning.
Then I had a call from e-bikes to send the whole bike back complete so I put it back together and everything is working fine!
I spoke to e-bikes direct later, again very helpful, and a chap from Oxygen, also very helpful, who had a good idea of where the problem could have been and to be on the safe side it's going back for a check up and the controller will be swapped out for a new one just in case it wasn't only just a simple cable connection problem.
I'm going to lose the bike for a week but if I don't it'll always be on my mind that it might happen again.
Impeccable customer service from e-bikes direct and Oxygen so far.
I will post back here what, if anything, is found to be the issue once Oxygen have diagnosed it.