When I try to make calls, it says ''Your call cannot be continued''. I haven't been able to make phone calls for the last 3 days. It is a problem with all numbers
I would try a new sim before you do anything else. See if that helps. Pop instore tomorrow if you can.
*The Game Is On*
Check for faults here O2 Service Status
and check this help thread Guide: Is the network down for me or everyone?
Track usage, upgrade and get support with the My O2 app