No internet trough cellular data, only one arrow is flashing, what should I do?

[60Dan06]

I got a problem with my Xperia Z2 (D6503, android 5.1.1). I cant connect to the internet trough mobile/cellular data, even if I got a full strenght signal. I can text SMS, I can call, but no internet connection. Whats strange is, that only one arrow (the upload one) is flashing next to the signal indicator in the notification bar. What should I do? I tried reinstalling the OS but the problem is still there