By Associated Press | PUBLISHED: January 16, 2019 at 5:27 am | UPDATED: January 16, 2019 at 5:45 am LAWRENCE, — Members of Massachusetts’ congressional delegation are criticizing Columbia Gas for a rate hike on Merrimack Valley customers affected by September’s natural gas explosions. U.S. Sens. Edward Markey and Elizabeth Warren joined Reps. Seth Moulton and Lori Trahan asked the utility company Tuesday to cancel a seasonal rate increase. They also called on the company to halt efforts to collect retroactive payment for gas service. The company suspended gas payments following the disaster that killed one person and injured dozens more, but the lawmakers say some residents are now receiving “sizeable” backdated bills due in January. A company spokesman said the rate hike is the typical seasonal adjustment made to reflect higher gas supply costs. He said impacted customers also will be offered “flexible payment options” and won’t face late fees or service charges.