Why can't I hear or be heard on one particular number?

[tommysmum6]

There is one number in my contacts that whenever they ring me or I ring them the call rings and I accept the call (or they accept my call) but neither of us can hear the other and the call rings off. We are both on EE and have been using the same contact numbers for several years. We can text each other without a problem we just can't make calls. It only happens with this one number. Does anyone know why? Thank you

[bristolian]

Does it make any difference, if you call with or without caller-ID?

I'd recommend reporting this to EE-CS - have evidence of 3-4 problematic calls over a 2-3 day period for further checks to be made. CS may well need to raise a faults ticket into networks.