It probably wouldn't hurt you to make a lawyer acquaintance and put one on retainer. A few hundred bucks upfront and you'll have someone you can call to help take care of things like this.
I can absolutely see myself falling into that same trap. Thinking that it's just a misunderstanding and that it'll get resolved any day now, just have to do one more thing. They can't be that unreasonable right? The unfortunate lesson that that you have to assume the worst and escalate right away.
This.
You need access to a good lawyer or you're going to get run over. When you sue, you can sue for legal costs, damages to your business, and punitive damages.