Though more facts may be needed, you should seek advise from a consumer attorney. Keep the letter and the envelope that it came in as the phraseology of the latter MAY have RFDCPA violations and it is possible that you may actually have a case. When trying to collect a debt, creditors have to be cautious in the language that they use. However, whether you have a case or not cannot be established without having all the facts and/or seeing the letter that you mention.
It is a shame that you do not have anything in writing - it is always wise to spend a little at the front end rather than a large amount at the end. But did you discuss what would happen? The real question here is, is he entitled to his $50K back or the value of half of the business. You need to sit down with a business attorney as this will take careful evaluation and not something that can be answered on a forum like this
I agree with counsel. You should definitely try and get a personal injury attorney. You should also look to see if you have uninsured motorist insurance under your own policy that can help you in making you whole
Because you're the owner of the car you as well as your son are liable.. So is your son an excluded driver or is he just not named as an insured on your policy. Those are two distinct things. I would contact your insurance company first to see if they can help defend you
Even though you fired your attorney over email, that did not necessarily release her by law. For example, if you were in litigation your attorney would still be your attorney until a signed substitution of attorney form was filed with the court. Therefore more facts are needed in order to advise you accordingly