Shervin's Independent Oil Center

After driving from Wisconsin to Wyoming a few weeks ago, I decided to take my truck to Shervin’s Independent Oil to get an oil change. I walked in and was very impressed by the detail the gentleman at the front counter went into in regards to what would be included in the service. I felt confident in handing the keys over to him and was pleased when I returned to find that everything had gone fine. He informed me that they had checked the belts, hoses, grease fittings, rear dif, washer fluid, oil, etc. I wasn’t surprised that everything was fine, because I had a certified mechanic inspect everything 100% before I came back to Wyoming. I paid the excessive 65 dollars for the oil change and went on my way. (I figured, you get what you pay for right?) A few days later, the truck started making noises, and wasn’t running to its full potential. I was concerned because I hadn’t had any issues like this in the past. I immediately went back to Shervin’s where Scott the owner was more than happy to drive the truck and take a look at it for me. He informed me that it may just be a loose fitting on the belt or alternator, but he would have to take a closer look. Unfortunately, he didn’t have anything available for a few days. So I contacted a few friends and found a respected shop just down the road. After looking at the truck, Leroy from 5959 informed me that I needed to speak with who ever had serviced the truck last. He told me that there was no rear differential fluid in the truck. He explained that the gears and bearings had been ruined and that it was going to be about 1700 dollars to replace. 
I immediately went back to Sherman’s to find out what had happened. Before raising a stink over everything, I asked the gentleman at the front counter what was included. He explained to me what they do for a routine oil change, and mentioned the rear differential. I then proceeded to explain to him what had happened with my truck and asked him how this was possible. He got extrem