Problem with mobile network

[Kalibar300]

Hi guys,
I have problem with my mobile network. My mobile network is on 3G and my APN setting working...
But when I installed WP 8.1 for developers my network is bad. Mobile signal is good but network is bedddd
How I can fix network speed? I have Ativ S i8750

 

[anon(7900571)]

which network do you have , did you tried contacting them , was it working fine in windows phone 8.0 ?

 

[Kalibar300]

Yeah, it worked fine on wp8.0
Maybe is problem in my mobile operator...