Business ProfileforDTIS Diesel, LLC

I brought in two PACCAR unit pumps and had them rebuilt, round trip 240 miles from Fresno. A day later, the pumps were done. I returned to Bakersfield and picked them up. Arrived at my shop and installed both pumps; they were inoperable. Called and they said there never have them fail. Advised me to bring them back. I drove back to DTIS, dropped off unit pumps. The following day they were done, I drove back again and picked them up. Installed both pumps and one was inoperable. I called and they stated that they were new to rebuilding unit pumps, but they rarely ever fail. They told me to bring the unit pump back. I returned it and the next day picked the pump up and installed it. The truck ran for three weeks and the pump failed again. I called yesterday and requested a full refund. They gave me $500 back out of the $1,112.50 they charged me. I called and they said they can't refund the tax or the 3% credit card fee. The tax alone is $82.50. They also said I had to bring back the unit pump to get my money back for the second pump. I clocked in over 700 miles and almost two weeks, lost a good customer, and now these jerks want me to drive another 240 miles round trip to get refunded. Who can trust this business as they have no problem taking advantage of businesses and refuse to accept any form of accountability for their continuously failed workmanship. Also, isn't it illegal that they would keep the $82.50 tax?