Complaint Review: MCI Worldcom Customer Relations

I have an International Calling Plan with MCI Worldcom to call
Barbados at $0.58 per minute.In the last two months MCI has started billing me at random rates.

In the month of (August)MCI Worldcom charged me $1.475 per minute for the month of July.
For (September)MCI Worldcom charged me $1.71 per minute for
the month of June.
Please note this is in the same order.
I first tried to call the 800 number printed on my bill which it
turns out to be Delta Airline Frequent Flyer Number.Finally my
local telephone operator connected me to MCI Worldcom.

I have tried to get this situation resolved by calling the MCI
Worldcom.I have called the customer service atleast 5 times and
each time they have not been able to resolve my problem and keep
connecting me to someone else.
The amount of money is quite large.
I am at the end of my efforts and I am hoping there is someone who can help me to get some assistance woth MCI Worldcom.
I am really desperate.