Your phone and iPad support dual bands? How did you confirm it?
Any other 5GHz Wi-Fi networks around that you can detect and connect to?
What kinds of phone? What's the version of your phone and iPad?

because i have this router, i have done the mistake to let it working in auto and in different regions than the one i am, my lg g3 cannot see over ch 48, but if the router choose from that band i will not be able to see it! check the channel that c20i broadcasts, and if it is over 48, change it manually.

@labrok

Right answer.

@FFK you need to log into the router and go to Wireless 2.4GHz menu to choose the corresponding region. Save and reboot the router. Then your iPad/phone should see the 5GHz Wi-Fi. If not, like @labrok said, you can manually set a static channel between 36~48. (I check the emulator on TP-LINK website and it shows channel 36~48 is available in Netherlands, if your iPad/phone is bought in Netherlands they should support the same channels.)