Mobile internet problem with unlimited data. Keeps disconnectiong after using 125mb

HELLO I have internet abonament on my phone, unlimited data. I have a big problem, I can’t use my internet more than 2 min, every time I have to turn ✈️ mode on and off and it works again, and I noticed that internet works only for 125 mb than I have to do that thing with ✈️ mode. And there is one more problem that I don’t get sms from Kpn with that thing that I am 80% of my data or 100% ...it îs a problem from KPN or…? I changed the phone and it’s same thing .. someone can tell me something? Thank you