Is $5,500 to replace a septic pump and install a new alarm a fair price?

I was out of town for work when an alarm indicated water under my sink. A contractor working on my house confirmed the water wasn't draining. I called a full-service plumbing company. After their truck broke down, they suggested pumping my septic tank. Two days later, they diagnosed my septic pump as dead and recommended replacing it and installing a new alarm. I agreed to the bare minimum, paying $5500, as they initially suggested $8500 in work. Upon returning home, I discovered that the original contractors had simply tripped an outside circuit, which had caused the septic pump to turn off. I feel they took advantage of my absence and didn't properly diagnose the issue.