I've dealt with a similar issue with a guy from Maine and me in Texas.

Do you have a letter, email, etc. which outlines the services to be provided, money paid,etc? Do you have proof the money was received? Do you have proof of an agreed upon completion date?

See if they are registered with BBB. File a complaint there.

Contact the S.C. Attorney Generals office and file a complaint there.

Send them a certified letter. Clearly and objectively list your concerns and expectations. Let them know you have filed with BBB and AG. I would also give them a clear and reasonable path forward i.e., return my money and guns by a given date or have service "X" completed by a given date with some means to verify.