You are in a strong position.
On this kind of issue, you can do whatever you want as
long as you don't break andy laws and don't break any
. If a review of all contracts pertaining to your
employmet (with the company and the recruiter) contain no
promise to stay and no penalty for pulling out, then it is
hard to see how they could justify any opinion to the
contrary. Of course, they might try to bluff, in which case
you calmly ask them to provide documents for proof. You
documentation of the broken employment agreement
should trump anything they can produce, if it came to that,
which I can't envision.
If you found the recruiter through a web site, check the
rules of the site. If the recruiter came to you, the story is
Your resignation letter should be brief and calm. "Because
of the change in benefits prtomised to me at the time of my
emplyment, I regret I must resign effective (date)."
I see no reason why you cannot present a conditional letter
of resignation, in which you request your benefits or regret
that you will have to leave. This is less clean, but it does
give them a chance to show whatever cards they may be
holding. You can send a copy of the letter to the recruiter,
with the documentation of the benefit offer and withdrawal.
He'll probably be glad to know they are playing games with
Hope your next job works out better. Good luck.