There does indeed seem to be a fault on their web server, so that all traffic is directed to a password-protected area instead of to the publicly-accessible site.
The company behind Polycell is actually Dutch, not German. It's AkzoNobel and you can use their contact form here for 'paints & coatings'
https://www.akzonobel.com/paintsandcoatings.aspx
or here for anything else
https://www.akzonobel.com/generic.aspx?div=CP
Alternatively, try a phone call to their UK division (ICI Paints AkzoNobel) in Slough: 0844 481 7890