The Minnesota Department of Commerce has launched another investigation into Frontier Communications, focusing on its billing and customer-service practices.

The Commerce Department said Thursday it is particularly looking at whether Frontier failed to inform its customers about their service options and whether the company enrolled customers in long-distance plans that they didn't want or use.

"We are concerned about Frontier's practices when customers are signing up for service and the prospect that Minnesotans are being overcharged for their phone service," Commerce Department Commissioner Steve Kelley said in a news release.

Frontier, which is based in Connecticut, said in a statement that it disagrees with the department's assertions.

"Billing and customer services practices were explicitly excluded from the previous settlement with the Minnesota Public Utilities Commission (PUC)," the company said. "We look forward to defending our practices with the commission."

The latest investigation comes just two months after the PUC approved a legal settlement between Frontier and the Commerce Department. The PUC began looking into Frontier in 2018 after hearing from its customers about poor service, from static-filled phone calls to billing mistakes.

Frontier, which also operates under the name of Citizens Communications, is Minnesota's second-largest landline telephone provider with about 90,000 customers, many in rural northeastern and southern parts of the state.

The Commerce Department on Thursday asked consumers to contact it if they have experienced issues with Frontier's service, including: having long-distance added without their knowledge or not being told by Frontier about cheaper long-distance plans; not being offered stand-alone local phone service; and being told either they cannot disconnect phone service without losing internet service, or that they can't buy internet service without also getting phone service.

In 2018, the PUC held several public meetings around the state and accepted comments directly from Frontier customers, getting more than 1,000 complaints (including 325 solely about internet service, with the PUC generally does not regulate). The PUC also ordered a Commerce Department inquiry.

The department issued a scathing report in January concluding that Frontier may have broken 35 laws and failed its Minnesota customers with shoddy phone and internet service, lax record-keeping and inadequate investment in its own network.

Frontier has denied breaking any laws, and in the legal settlement it didn't admit to noncompliance with state regulations and statutes. The settlement calls for refunds for aggrieved customers and establishes a framework to deal with any future Frontier phone service problems and maintenance breakdowns.