Service Issues - Advice please for a newbie!

Hi I'm new to caravanning and the CC and just wanted to ask people’s opinions and experiences.

Having bought a nearly new outfit at the end of last year (private sale), I booked it into my local dealership for its service to maintain my manufacturers warrantee.

I asked for the battery to be changed as an extra job, as it was not holding charge.

On return, the tray, compartment, door, door seal and wiring were all wet with battery acid. There was a 2"+ split in the main positive wire insulation with the copper exposed and even worse at the point where the outer insulation had been cut back both the positive and negative wires were nicked to the copper wire, only millimetres apart (and obviously not protected by a fuse at that point, if they had come together, which was likely as the negative terminal was also fitted incorrectly, 180 degrees the wrong way and the wires were under stress at the outer insulation join, they it would have shorted the battery and caught fire).

Additionally, I was charged for a new water filter (which I don’t believed was changed, as the one on the end of the hose, external in barrel type, was still wet from last use and my recollection is they come dry with instructions to wet them to ensure they sink in the barrel) nor did I want it changing, it was only a week old,

There were some other issues, but I’ll save them for now.

I have spoken with the dealer and sent them all the photos.

They apologised and said they would sort out 'some' discount for the next service.

But they want the caravan back for some further warrantee work (for which I think they are doing as a matter of course rather than due to an actual fault being found as at least one of the wet lockers where wet was found under the tray, had "had the tray removed" somehow without unpacking the locker and breaking the old dusty cobweb in there), but I’m not sure I trust them, especially given my complaint, but there are no other local dealers!

Should I leave it at that?

Should I ask for some money back (£350 for service and battery)?

Should I contact the Manufacturers?

Any advice would be much appreciated!

Name of dealer witheld.......for now