Other parties insurance recommended shop damaged my car more…now we are stuck with endless back and forth need advice please

Hi everyone I need advice for auto insurance in California. Both of our insurance determined the other party was at 100% fault for the accident. Their insurance is All state. All state recommended me their partner shop and told me they are Benz certified and car would be fully fixed. A month goes by and I am told my car is ready to be picked up and my dad goes to pick it up and after coming home I noticed that it is missing trim pieces and the door involved in crash doesn't close all the way and the door not involved in crash has swirl marks all over. I took the car to a Mercedes Benz approved body shop and they quote almost $10k of damages that needs to be fixed and so far its been 2 months and All state Admin keeps saying that the shops have to be the ones to negotiate but their partner shop is just delaying it.