Unfortunately many banks are only concerned with selling their houses and not with the hardships it may be causing the potential buyer.
As Dianne said, based on the information you provided they probably acted legally but perhaps not ethically.
If the predictions are accurate, the flood of foreclosures yet to hit the market but will put you and other homebuyers in a much stronger negotiating position.
The right home for you is out there, but market conditions make it a bigger challenge than ever before.
Hang in there!
It is sad to hear of this.
Perhaps the offer that was signed, was conditional upon the addendum being signed.
I hear time and time again that banks do things that are unethical.
You may want to stay away from banks and deal with people, a regular standard sale or a short sale.
Keep your wits and patience about you.
This is one of the most competitive times for buyers in years.
So Cal Homes Realty
I would need a little more info on what were the addendums. But.....If it was the bank addendums that come after your offer, which is really a counter offer then yes, it is legal. Until you signed them, your do not have a meeting of the minds (it is not an accepted offer). During this period they can accept another offer. I am sorry and I know it doesn't seem fair but to banks it is just business and they will do whatever it takes to get ahead. I personally don't think it is very ethical but this is really a cut throat time.
I can only say that I hope you find something better and then you will be happy it happened. I wish you the best!