The reply that you received,
man there is no excuse for an answer like that!!!
Your reply should have been more like you can use any denomination or amount of stamps as long as the total equals at least the $2.68 price point that you figured. If you go a penny or two over no harm no foul, other than you are wasting your money. If you go a penny under you run the chance that a number checker will catch the shortage and send the package back to you.
Be careful using "forever" stamps. They are only worth what they were worth at the time of purchase and NOT the current First Class Letter value. So if you bought a bunch of "forever" stamps when a letter was 45¢ that stamp is still worth only 45¢ today. You will not be short if you use that stamp on a letter but you will be short when you use that stamp on a package expecting to get 49¢ for it.
The PO makes BIG money printing stamps that never get used! There are a lot of collectors buying up those paper stamps!
As to your point of printing postage on line, that is recommended even buy the PO. They do not have to pay an employee to service you when you are servicing yourself. Your computer is open 24/7 and you can print postage in your pajamas and have your carrier pick up your package at your door the next day at your normal delivery time.
You do realize that you can print shipping labels on line at
www.USPS.com as well as many other on line postage outlets and pay for them with your credit card or PayPal? You may never go to the PO again.
The person that handled your inquiry must have failed math. Maybe the schooling is better overseas and when they outsource customer service maybe then they will get it right? [sarchasm!!!]