It’s your debt & your responsibility
It is YOUR responsibility to make sure your medical bills are paid. Medical providers process claims to insurance companies as a courtesy for patients. It’s fairly common for bills to not get paid and bounce around for several years. It’s YOUR responsibility to check those benefit statements the insurance company sends and make sure the medical bills get paid.
Not receiving the bills is no excuse. The unpaid bills are eventually sent to collections, and once they get there your credit is affected.
As for the bills that are already in collection – the damage is already done, and even paying them won’t raise your score. You may want to try a pay for delete agreement, but it’s really very hard to actually get the collection agencies to cooperate.
In the future, keep better track of your bills and make sure they are covered.