Am I understanding you correctly - you are in escrow selling a home and are waiting to purchase another. But because of the delays, challenges, and (very late and unethical) advice of an outside party/agent, you now want to cancel your buyer (with whom you are legally in contract of which you are bound to its terms) so that you can, according to a promise from this outside agent, close faster?
Is that correct?
If that is correct you need to first communicate this to your agent whom you hired to carry out the sale of your home. Revisit expectations and responsibilities. Give him/her an opportunity to address your concerns and frustrations.
If that doesn't work, have their broker intervene, & then the final course of action (due to your time constraints) would be a real estate attorney. Have them review your contract to see if/how you can close with the current buyer. Or if necessary, how to legally terminate the contract.
Hope that helps.