Model : TD-W8970B

Hardware Version : V1

Firmware Version : TD-W8970B_V1_150526

ISP : Telekom SK

Recently i have changed my dsl router to enchance the functions and coverage.
My "precious" is now the TD-W8970B.
Everything worked fine until the moment when i have connected my smartphone.
The wifi icon stays grey instead of turning to normal blue.
I can browse the internet, google play works also, but
the facebook, facebook lite apps are connecting very slow or dont connects at all.
Therefore i dont get notifications from facebook and/or messenger.
At work or other places the wifi turns to blue automatically.
The Googled "solutions" (hosts file edit/delete, rooter reset, phone reset, changing dns in rooter, lowering wifi security)
ar not helpful.
Am i overseeing something?