Welcome to CHR, and as Glenn says you're starting off with a tough first post. I already voted on the poll, but thought I'd offer that I think Glenn has the right approach. My initial thought was that you did not tell them you wanted a roller cam block, so you got what you got, but you may well be able to work with them and get some parts at cost, or some benefit by agreeing to work with them. Admit your mistake, and ask if there's any way to turn a bad situation into something that works a little better for you.
Good luck, and keep us posted on the outcome.