I got it from Direct Choice, who I have my car insured by. When you get a quote from the AA for car insurance, they ask you right at the end if you want to be put through to Direct Choice for a quote. I'd phoned several 'known to be cheap' car insurers and I got £270 as the best quote. Direct Choice insured me for £170! They may well be dodgy though. I'll blame the AA if they are.
I just googled and found Windscreen Insurance Services Ltd's number on a PDF page here:
https://www.directchoice.co.uk/PDFs/Glass%20policy%20wording.pdfIt gives it as an 0845 though.
Did try 0844 8000026 earlier today and got through to their answerphone.