Thank you for all your advices, but I honestly tried everything. I hard resetted my router and phone, I went through all the settings, and still the same. At this point I'm just waiting for a miracle.
Thank you, but my problem is that the connection is slow on my phone, not that I can't connect. And It was good until yesterday, and no settings have been changed. That's why I don't have a clue about what's the problem.
My router only has one band, and I didn't find anything about smart connection in the settings, so I guess it doesn't have that feature. Also I did a hard reset on my phone out of frustration, and it didn't help.
I'm OP
Thank you, but I already rebooted my phone several times, and even did a cache wipe, and I already rebooted, and resetted the router several times, and still no luck.