Calls dropping and silence from incoming and outgoing

[Paul74]

I have been in contact with Apple who ran a diagnostic test on my iPhone. Calls are dropping out and sometimes there is just silence. Also when I receive calls they can hear me but I can’t hear them. I have reset all settings but nothing works. 

[MI5]

@Paul74 

Try a new sim which you can get from any O2 store for free (take photo ID with you).

Also check guide Guide: How can I sort out my network issues?