Phoned and spoke the service "advisor" 3 times over the following weeks, each time received a "I'll find out and call you back".
This week remembered that I had again not been phoned back so sent a mail to the service contact shown on the website - Joe Jones.
I got an immediate response followed a few hours later by the mobile tech installing my air filter at my house
So yes every right to be irritated by earlier bad service, but Joe restored a bit of faith by his decisive actions.
I still think Imperial is stuffing things up but let's hope it comes right.
Cheers
Tom