Austin Publishing Group does not seem to be a reputable publisher. You should stop communicating with them immediately, because so long as you respond to predatory publishers, they have an incentive to keep trying to manipulate you and induce you into paying them. They will generally try various negotiating tactics and will never leave you alone so long as you keep up the communication. I think you should simply ignore them from now on. Since you have not agreed to paid the fees, and have clearly communicated that you will not be able to pay even if you have to withdraw the paper, they cannot do anything against you. Just make sure you have all the documentation saved somewhere as evidence just in case there is a problem.
A word of caution for you: Do not add this publication to your CV or researcher profile as you would not want to be associated with a predatory publisher. This can affect your credibility and reputation as a researcher.