Confer with attorney legal rights, show executed agreement.
Sorry to hear about this.
Bright side of it as you may consider staying until after the fact it is foreclosed and Lenders agent contacts you to vacate the house and then you may show them the contract that you had and try to buy directly from Lender.
Ask the present seller to talk to the lender and tell them you will like to buy after if they are willing to consider to help you!!
There are several ways if you are proactive..
yes, you may try going to auction too and bid but usually they price it too high there.
Is the closing taking place before the auction so debt will be cleared?
Have you contacted the office handling the auction to learn the details?
In this area.....seller can stop the auction the evening before it takes place by paying off the back taxes and fees.
And of course....you may want to contact your attorney.