Put your final offer in writing, have seller sign and submit.
Sorry to say most banks when negotiating prices do it verbally ( that doesn't make it right, it's just the way it's done ) What I would have my agent do is if the bank verbally gives you a counter offer and it is acceptable to you THEN put it in writing, or have the bank put it in writing to sign by both parties. This is how it is usually done.
I'm sorry to hear that you are being "jacked around", but that happens sometimes when dealing with banks.
I hope it resolves for you,