Accident responder’s insurance does not want to pay full reviewers and rental cars

Hello everybody, in December someone drove me in the back when I was standing at a red light. (Accident was clear: the other one was to blame.) Then I brought my car into a free workshop. This then also commissioned an expert, organized a rental car and repaired the damage. Was all so good. Now I got a letter from the opposing insurance company that it is not ready the expert costs as well as the costs for the M In your opinion, these are disproportionately high. What should I do now? It can’t be that I still have to pay what after someone drove me in??? I have left everything organizational with the insurance, evaluator etc. simply to the workshop in the assumption that it will probably know with the procedure in such cases. So… what to do now? Thank you & best regards, Michael