Help!

I've just set up a Deco P9 today. I'm on Virgin Media and have 350mb broadband. I've got everything connected and running however I am only getting around 100mb on devices. I have wired via ethernet to the main deco and the speed to that is 367mb. I think I need to get into the deco settings and change to 80 to open up the bandwidth. I cannot log on to the web interface. I have tried via the ip address, tplinkwifi.net, tpdeco.net...all I get is cannot connect to server. I have spoken to livechat and they said I needed to update the deco, checked and all up to date. I have called their support and they were useless saying I cannot change settings on the router...cannot change ports etc. I have said I need to log in to the web interface and get in to the router settings, he said that is not possible and who told me i needed to increase the bandwidth....arrrgggghhh

Can anyone help. I can't understand why I cannot log in to my router. I think the bandwidth is set at 20 or 40 and therefore I will only get around 100mb but need to change to 80. I am using my Hub 3 as a modem only