iMessage problem unsolved

I can’t activate my iMessage, tried everything found on internet, I mean everything, and still can activeate after every method says unsuccessful activation and greyed number charging. I have an iPhone 6s Plus updated from iOS 9 to iOS 11.2.6, and maybe this is the problem, and I don’t know what to do it s getting annoying after 2 weeks still can’t activate iMessage, I repeat, I tried everything.