Rip off

Had to buy another computer because I had a computer using Windows 10 and it could not be upgraded. Brought a new Dell computer with all the triming. Dell said they would buy my old computer.I gave them the service tag number for the old computer. They gave me a price for the computer and I shipped it to them. About a month or so later I received an imformation from them stating they had made a mistake and they dropped the old computer price $100.00 less than stated. On top of that the remaining money was added to the Dell Rewards program which I had no idea existed. I later, after opening an account with Dell Rewards,realized I could only use the balance  as reward points to purchase Dell products. Again let me state I had just brought  a new computer system with everything I needed and had no use for anything Dell was selling. Dell has now emailed me to tell me the reward point will expire in a week. So I gave up a working computer to Dell for nothing in return, at a value they conveniently reduce after having all the information on my old computer system. If that isn't a sham what is!!! Taking steps to try and get some satisfaction from Dell but not holding my breath. Wish I had just donated the computer to our local charity as I had wanted.