Calls, sms, email don't work, or delayed with hours

[csillu987]

I bought my S3 mini a month ago brand new. About 2 weeks later I had difficulties with calling others, it was dialing but no ringing. Others also could not call me, and I got an sms (sometimes an hour later) that I had a missed call (like if the phone was off). Then I could not send smses and emails got stuck in outbox and were sent middle of the night while I was sleeping, hrs later. I took the phone to the Samsuns service and they did a quick software update. The problem remained so I left it there for a full reinstall. 2 days passed and I have problems with calls again... What could be the problem? They said I downloaded something, a virus or such. I only downloaded a few standard apps, like Fb, Twitter, MyUploads, WhatsApp, Viber. I cannot accept the answer they gave me that I downloaded something with a virus coz in 2 days I didn't download anything other than these few apps. I think it is the problem of the phone. Does anyone else have similar problems?