Something like that happened to me. Guy sold a leased receiver. I even called Dish with the number. The CSR reversed the last 2 # and told me it was clean. Sure enough, when I tried to activate it, bad news. Dish did help me out with me sending the leased receiver to them (at their cost) and them giving me a 625 lease, but dropped the lease fee for 18 months as sort of a "reward" for finding & sending them their leased that I bought!
Hopefully you paid through PayPal. File a claim NOW! That should get the sellers attention and maybe you can work it out. Worst case, the seller doesn't respond & you get your $ back (thats what happend with me, got every cent, including shipping charges, refunded to my CCard).
I learned my lesson! I WILL NEVER BUY ANOTHER RECEIVER ON E-BAY, EVEN IF THE CSR AT DISH SAYS ITS CLEAN! Visit one of the sponsers stores I will!
Best of luck!