Stoj - I am sorry to hear about your predicament. The good news is that your Diamond is GIA certified, which means that it is legit. Do you still have the diamond report - so long as it matches up to the laser inscription on the diamond you are good to go.
That bad news is that he jewler in Batavia stuck it to you. However, with how he marks up his jewlery, he should be more than willing to give you $2500 for the stone and $500 for the setting.
Here is what a similar round diamond is going for on Blue Nile. (for any posters looking to get engaged, I bought my wife's ring on Blue Nile and got the highest quality and best price by far).
Carat 0.91
Cut Good
Pol Good
Sym Good
Colr G
Clar SI2
Price $2,710 (Price per carat) $2,978