Counter Offer Accepted, then Rejected?!

[Chris Bellomo]

I need advice. I made a best and final offer, along with 8 others, on a duplex in my local LA neighborhood. My offer was for $911,000 but a few hours after submitting, after a discussion with my agent, I increased my offer to $921,000. The following day (today), I received a signed acceptance of my final offer of $911,000. I was surprised and thrilled and figured the buyers were never presented with my higher offer. I docusigned my counter offer and sent it back 15 minutes after the 1pm deadline. (my agent sent me the document only an hour earlier)

Now the sellers agent is crying that he made a mistake for accepting the lower offer and that my acceptance 15 minutes after the deadline disqualifies my offer but they will use it as a back up.

I'm crying foul. The sellers were presented with an offer that was acceptable to them and signed it. I countersigned in a timely manner. I feel the agent is muddying the waters because he is looking for a higher offer. And if he messed up, he or his office should pay the seller the difference, not put me in a subordinate position.

What say you and does anyone have insight into the California real estate contract law aspect of this matter?

Much appreciated!!