HI, I cannot call for days another number (a mobile number ,overseas), and the only message I get all the time is "We cannot proceed with your call due to congestion". This regularly happens any time during the day - I was using two of my mobile numbers.
I am having the same problem with both, and both of them are prepaid.
I am not sure what is happening. It would be greatly appreciated if you could resolve the issue as soon as possible.