That all sounds legally valid. ————————————————————

Look into a motion to set aside the judgment for failure to lawfully serve the lawsuit.

Selected as the best answer

It may be difficult to do so. Contact the creditor to work out a payment plan.

It is probably adequate service. Note, You must respond in the legal way and on time with, for example a motion or an answer with affirmative...

The plaintiff knows you responded so they should not take a default.

Any of that is possible, except you will not go to jail.

You can prove “failure of consideration” and no “meeting of the minds” and no agreement made.

While such a case is unlikely, it is theoretically possible.

Please repost your question with different words.

Yes. All parties must be served. ————————————————