Difference in Business Service Order Agreement amount and monthly billing statement amount.

After having made three phone calls to customer service, I have yet to receive a satisfactory answer as to why the "Total Recurring Monthly Bill" amount ($159.75) is significantly different from my actual monthly bills for the past two months, ($198.55 for June and $201.60 for July).  These bills are approximately 21% higher than anticipated.  Someone please explain and justify.