The irony is that if you call after you get your ECoPR, you will get connected to an agent immediately. It happened to me.I guess it is a queue system which everyday handles lots of call the same time, so even the queue is full, then it will give the 'our agents are busy, there is no available agent'.
Just do it again and again, and there are some tricks to make it easy if you want to search this thread back a few page, lots of people here are sharing their experience and suggestions.