Jump on that settlement
Judgments don’t just go away. If they agreed to settle for the $550 you should jump on that.
Even if the judgment is was given in another state other then where you live, they can file the judgment in your state and proceeds to garnish wages, attach your bank accounts, and lien personal property. Once they domesticate the judgment in your state, they won’t be accepting any settlement for less than the full amount.
As to the house you were looking into – mortgage lenders won’t approve a mortgage until that judgment is satisfied. Make sure you get a settlement agreement in writing before you pay.
Make sure that the settlement includes their commitment to file files the satisfaction paperwork with the courts. They are the only ones that file the paperwork, and if they don’t – your credit report will not update to show that the judgment was satisfied. FYI, it will take some time for all that to process and show up on your credit report.
It is true you could try to have the judgment set aside if you never received a summons, but you would have to hire an attorney. Since this is actually your debt, the collection agency will likely just serve you a summons right in court when the current judgment is set aside. So in the end, you might spend time and money just to end up with the same results.