When we moved back to BT last year we had similar. He had wired the phone line side back to front. Tried to accuse our internal wiring of having issues that had been fine for donkeys years.
but I noticed a post the other day (here or thinkbroadband?) where the answer to such a complaint there was effectively 'The retailer's are our customers so they must make the complaints. We ignore any complaints made by end users.' Still, maybe they'll accept the praise for the good engineer?