Siemens Gigaset Repeater Wlan Se365 Boosting Wifi Signal?

I recently purchased a Wi-Fi repeater (Siemens Gigaset Repeater WLAN SE365) to boost my wi-fi signal throughout my house without having to drill through walls of concrete (with a boost in phone wi-fi in mind on the top floor of the house). I was advised to buy one specifically with the make and model of my router in mind, as connectivity might be an issue if these don't match up. I own a Siemens Gigaset SX55 router so there should be no issue there (I can use the repeater on 2 different frequencies, not sure which one is best, 2.4 or 5 ghz). The instruction manual told me to connect the repeater to my pc once (through use of an Ethernet-cable supplied) so I could alter the settings of the repeater to match with that of my router (same SSID, protection method, channel). Whereas naming it the same as the router by modifying the SSID and using the same ASCII WEP-protection password as the router were doable, I could not find an option to change a channel.

At this point the instruction manual was fresh out of ideas and told me that I had set up the repeater as it should be installed. After unplugging it from my pc and plugging the regular ethernet cable back in for internet (There is wi-fi coming from the router downstairs but also a cable through the house to the pc) I was ready to go and seeing the wi-fi bars on my phone jump up to maximum made me extremely happy. Unfortunately the phone (and the app Wifi Analyzer) did recognize the full signal but when trying to open sites or apps that use internet it responded as if it had no signal whatsoever