How can I tell if I was given old pain medication from the drug store? I was given generic that I didn't want?

My pain is chronic. I am inoperable. My pain is incurable, the cancer like pain has rendered me bedridden. At this stage I am just to be made comfortable.My spine is being eaten away. I have been on percodan many times, I know the texture and how well it works on me. My last pain medication for the last 4 years has been vicoprofen. When I told my dr. at the pain clinic that the vicoprofen has not been effective for about a year he put me on percodan. He wrote the script and my husband went and had it filled. The room was dark when I took my first pill but in my mouth the pill just fell apart, began to dissolve and I spit it out. I took another and the same thing happend. When I checked the pills they were yellow, I had never taken a yellow percodan before, they turned out to be generic. Second the pills did not take care of the pain at all, never even came close. I called the pharmacist the next day and told him these pills are not any good. They did not help my pain what so ever and that I thought the pills he gave me were old and did not even look like percodan. He argued with me and said he gave me generic because they stopped producing percodan and gave me the substute. I found out 3 other drug stores that I called had regular percodan on their shelves and none of them had heard of the discontinuation of the drug. he lied to me. So if he lied about the production of the pills he could have lied how fresh they were also. I have never, ever taken generics and have never taken old medication. My questions: Are old pills affective? Do old pills dissolve in your mouth? How does one really know if they are taking old medication from the drug store?