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The answer to this depends on what type of contract you had with the old agents and what kind of clauses were in there.
Second, talk to your current agent and the old agent who brought the buyer. If you can negotiate between them, this may all work out.
The other option and your bargaining chip is that you can just take the property off the market before any offer is made or you can reject the offer.
Rejecting the offer for the actual offered price can get you into semi-trouble but you can put your in your contract that the sale of the house depends on your ability to gain a mortgage for your new property so unless you are able to get a mortgage, the sale will not go through.
But in this case, I think strategically try to negotiate with the agents or tell them you will be forced to take the house off the market (you may want to take the house off the market temporarily to make sure that nobody tries to put in an offer just to spite you). Once you have a signed agreed contract between all of them, then go ahead and accept the offer.