Can you help me? Please!

I’m doing a job for a client. It’s my first one for them. They ask me to bid a remodel on a house they just purchased as an investment property. I submitted a bid to them and they asked to meet with me to go over it and nail down some specifics. I did and it turns out the bid was higher than their budget. So, knowing that we went through and I made a new bid that would accommodate. Things went smoothly for the most part. There were a few here and there’s like using green board vs Sheetrock, specific screws, and there were some things they asked for my help with that weren’t in the bid like removing the bathtub for the floor guys as well as the toilet. Then there were some things that had to be done like pipe leaks, etc. so about 1/2 way through he called and said that he wanted me to get a crew. At this point it had been me and my son who is 17. I reminded him that we lowered the bid to accommodate him and that really cut out a lot of labor. He then said it was unprofessional for my son to be with me. Keep in mind my son went the 1st day along with the fence guys that work for me. They removed the part of the fence that I was instructed to remove and he helped me move a cabinet. Then he sends me a list and says he thinks it’ll help me. But the list is what I’d have done if I was doing the 1st bid. So I tell him. I’m not doing it like that. We agreed I’d fix some issues inside, paint, do exterior. Basically white box the inside. Well, he really doesn’t speak to me much from that point. Then I have 3 days left. 1 inside and 1 outside. He comes by with his wife. Seems normal and they leave. Next morning he sends a cease and desist. States I’m not performing work to his standards, my son is working underage, and I’m working late and on weekends. When I started I explained I’m really busy and if they want me to do it the schedule will be sporadic. They agreed to it. So I message them to let them know I will have my tools removed that day. Later that day he asks if I will clean the paint off the tile. I say ok and I message what’s left and I thank them for the opportunity. He messages me again later and asks me to hang the kitchen cabinet doors. I told him I’d call him later. I did, no answer. I sent a final invoice for work I had completed. Since then he has asked me for the deposit, he’s filed a claim against my general liability, he’s telling them that I have ruined the tile in the whole house, the cabinets are ruined, that I broke sink valves and damaged things, all kinds of stuff. The day I gathered my tools I took lots of pictures. None of that is true. What can I do to make this guys stop and to pay me what he owes??