Garage Door Repair 24/7 Quoted me a price then charged for "service charge," telling me first it was labor then saying it was tax Internet

I asked for a complete price for garage door repair. They quoted me a price without mention of a service charge. I ended up signing the bill and paying them without noticing a tacked on service change. I called up and Tom told me it was labor. Nonsense -- the labor was included in the price of the springs etc. Later, they changed their story and told me the service charge was tax, thereby violating NJ sales tax law regarding the recharacterizing of tax as a service charge. Also, the service charge they claimed was a tax was levied at 7 percent even though the NJ sales tax is 6.625 percent. I asked for the return of the service charge of 117 bucks. Now they are ignoring me.