If it is actually your bank account, speak to your bank manager.
With Paypal, if you are buying in US dollars there will be foreign exchange involved. This changes rapidly, although most banks only change their rate daily, fudging to allow for the hourly or even minute by minute changes in the world money markets.
The loonie has been dropping, thanks in part to our PM's indulgence of the oil sector over the manufacturing sector, and we are now in recession.
So between the time you buy and the time you pay, the exchange rate has changed.