Losing network operator on Samsung Galaxy SIII mini

For some time now (I think it's from the latest Android update) I have this problem, that time to time (on daily basis) people can not reach me, like I would lose connection to the Network. I get an SMS after some time about all the calls I did miss. Sometimes I have a hard time to call as well. I did call my operator, and they didn't had any report like this so far, and I did call Samsung service, and they didn't know about this issue, so I guess is on my side. If you have any idea what would the problem be let me know.