I would write a lengthy, but polite, letter to the service manager. Explain you are long time repeat customer (hopefully, you are), and if they don’t make this right by refunding your money in full, you will take your business elsewhere. The last time I did that, they mailed me a check for the full amount.
Losing a few hundred dollars is smarter than losing your business permanently. Take advantage of that logic. Tell them you paid them to solve your problem, not throw parts at the problem.