By Katie Westwood A woman was left stunned after she received a debt letter for a British Gas bill that dated back nearly two decades ago – a mistake for which the energy firm have now apologised. A debt collection notice left 60-year-old Gillian Evison from Thornton greatly distressed. On April 22, she received the letter from Capital Resolve, stating she had an outstanding bill of £414.72 to clear with British Gas. The note demanded: “It’s time to pay your British Gas bill of £414.72.” Gillian told the Liverpool Echo: “I felt upset and shocked. I’d never received anything like that before. I…