So this is likely one of two things: a clog in the line or the sewer line between your house and the service is broken. You didn’t say how old the house was, but the older it is, the higher the chance the line is actually broken (especially if you have any drainage issues near the foundation or foundation settling issues). No matter what you’ll likely need to figure out what the issue is first by having it scoped and then figure out your next steps. Hopefully it’s just a clog!

Source: had a broken line in a fifty year old house. It was awful and definitely not cheap.