This is not legal advice but it appears by what you posted that the broker is not entitled to a commission in this case.
You need to find out if you are dealing with the agent or the principal broker of the company. They are not allowed to hold or control funds in the event of a COMMISSION DISPUTE. They would need to take formal action against you with them as the principal broker but still perform their duties. If this is just an agent in most states it is not their call to even take action with a commission dispute. It is not their potential commission but the principal brokers.
Now sometimes sellers do not know that the buyer found out about the property through the marketing efforts of a broker. For instance a buyer might see something somewhere on the internet and then try to contact the seller directly or talk the broker and then call the owner directly after saying they were not interested.
So it is entirely possible that this buyer said the found you directly but actually found you through mean of the broker. Also the LLC and other transfers before it if the buyer or buyers are connected the broker could argue they are owed a commission.
So I am just throwing that out there where a seller has told me before I talked to so and so and I have this buyer and I say yes they called and found you through my marketing and I have the date and time etc I talked to them and other communication.
Some buyers will lie and just want a property however they get it and do not worry about collateral damage or duties the seller might owe in a listing agreement.
At this point really I would get an attorney at least to send legal communication to this person if they are the head broker or if they aren't send a copy to them as well as the principal broker outlining what has happened etc.