I won't bore you too much with this one, just get you up to speed.

Stopped paying in 2010 and sent cca request to Citi. Had a letter back saying they were unable to find the agreement and therefore the account is unenforceable.
Opus then took over the account. I challenged them to supply an agreement, but all they did was send some current terms.
It went around the houses and Cabot purchased the account.

I sent Cabot the CPUTR 2008 letter asking them if they had the agreement, but no answer forthcoming. I did not hear from them for literally months. They then sent a statement and asked for payment. I challenged them again and received another set of current terms from Opus, along with a recon.

My question is, what now?
Is it time to show my hand and send them a copy of the letter from Citi which categorically states they don't have an agreement?

Thanks again.