Go Assist - Cooker Hood not extracting.

I filled in a form on line to Go Assist since my Bosch Oven Extractor Fan was not extracting but the electrics were working. Paid £149 up-front. First they sent an electrician who arrived at quarter to 9 one evening to say electrician was not required! Send an engineer. Who came promptly with little English but did take the flue chimney off and said I needed a builder. Called a builder in myself independently and the extractor was a recycling one and it required new filters. Should the engineer not have known this when he looked inside? No rebate or re-visit was offered "since we sent two visits" . Not happy