After paying what a surgery center said we could pay for an outpatient surgical procedure, we were billed $3000 more and civil suit and subpoena

We had an outpatient surgical procedure done. Upon arrival the surgery center said we could pay a certain amount that day and be covered. Documentation is available. A couple months later we received a bill for ove $3000 for the use of the facility. Our insurance company claims they requested additional information and never received it. Now we have a civil suit pending for this amount. What can we do??