Frontier Communications has failed to properly maintain its telecom network in Minnesota, leading to “frequent and lengthy” phone and Internet outages, an investigation by the Minnesota Commerce Department found.

Despite that, Frontier has failed to provide refunds or bill credits to customers affected by outages that have sometimes lasted for months, the government report said. Frontier is also guilty of frequent billing errors that caused customers to pay for services they didn’t order and has failed to promptly provide telephone service to all customers who request it, the report said.