I suppose it depends if you've signed any contract from the garage? and what that says. A deposit is usually just that, and thus if the garage has found an issue they are usually within their rights to return the deposit and make sure you aren't out of pocket (I doubt the trailer would come under this).
However if you've signed the battery contract then that could be interesting, as legally you now have no car but could in theory be responsible for the battery.
First thing I would do is to ring RCI (Renault Finance who your battery lease is through) explain the situation, firstly make sure you are not going to be charged for a battery you cant use but more importantly make sure your credit isn't going to be affected by this cancellation of a lease contract.
(Ask to be transferred to the ZE department when you ring as the general finance department imo haven't a clue about battery leases)
Good luck, again I would suggesting ringing Jessica Evans @ Renault customer services and telling her how rubbish your experience was. I recently told her Renault has no idea how difficult/annoying it is to buy, insure and service a Twizy, this should hopefully confirm that again.