Hi, recently experienced the problems of the tendency not making or receiving calls. I downgraded the Internet setting through the andriod market Giffgaff apps, and everything worked just fine until I could not make calls a week ago, tried to call my mate but nothing happened, then tried to use my girl's phone to call myself, and right through the voiceover, however I could receive text messages, and about an hour late, it worked.
This morning, my mate tried to reach me by calls and texts, I did not receive anything until lunch time. All calls went to voice mail and texts received about couples of hours later they sent, Its quite annoying that you get a phone but not working all the time,
Hey check your Signal bar
delete your current settings and text
"settings" to 2020 without the quotations.
Enter in your settings your self by a tutorial below.