SoloSuit

I got served that I was being sued for a debt by a collections agency. I won’t get into specifics but the debt amount is essentially incorrect and I did not pay as it was not a fair amount. Nevertheless I used solo suit to file an answer, filed everything with the court in person and sent certified mail to the opposing lawyer. A month later I get the certified mail back saying it was refused by the lawyers office, and then a letter from the court that the case has been defaulted because I never answered. I am lost as to what to do now and how the default was even granted given the fact I did answer the complaint. If it helps I am in the state of Idaho.