I do not make international calls, but sometimes long distance. I have Verizon as my carrier, but I may be bias'd in that I am a tech for them. I did not know the rates for your area or availability, but try
www.verizon.com for info.
Can you make calls to other cities very close to you, that can be local long distance? If so it sounds very much like it would be Excel's problem. But if you cannot call out of your exchange, it sounds more localized. Keep in mind most "small" or low rate long distance companies use our networks to carry the calls. The FCC requires us to sell to them at lower rates than it costs us to operate them. The problem is getting the smaller companies to "find " the problem. This requires them to make several calls and go thru extra "testers" to isolate the trouble. This is not the case with larger companies in that you call the carrier directly since you are our customer.
To make a long story short, it eliminates the middle "men" when it comes to repair.
Good luck, that is all the help I can offer without getting myself into any problems.
If in any way I violated any GBO rules please delete and let me know.
Jerry