recently had work done on gas boiler. gas fitter told me system needed cleaning. asked for estimate. got written estimate of 56.00 pounds. asked them to go ahead.when i came home wife said he had fitted magnet to keep system clean. looked up on internet to see part was 110 pounds. realized they must of made mistake with estimate. now got invoice for 560.00 pounds. any advice. ? would not of gone ahead with work at what there asking for. (key board pounds sign not working)