MPG has just fallen of a cliff after service

[DXX]

I hope they didn’t think the ‘failed’ MAF sensor had put it into limp mode and caused the excess fuel consumption?

 

[JOG]

You’re very restrained in not naming and shaming already! If I was writing the email, it might contain some words that rhyme with “cough”!
This is a job for a visit and a discussion. If you paid with a credit card, I would be inclined to put the transaction into “dispute” with the card company and also consider small claims court.