Take good pictures of the battery compartment ASAP. Touch nothing. Call RV Service company and tell them what happened and tell them you need a qualified battery installer. They will not be surprised their Tech screwed up. He may be new on the job. Give them the chance to fix.
Have you paid them? If you used credit card, I will file a claim that serves was note rendered and you are waiting to for them to come back out.
If you paid cash
How much you paid is relevant. The more information you provide, the better help you can get. Pictures may help someone to see where or how it is wired wrong.