Canadian Dollars

A question about : Canadian Dollars

Hi all
I'm looking for some advice concerning some Canadian Dollars that belonged to my aunt.
When she was taken ill and moved to a care home my mother took the dollars to the post office to get them exchanged to pounds sterling. The post office exchanged some of them and handed some back saying they couldn't be exchanged.
Now, I'm don't why they couldn't exchange them and I'm now trying to find out why.
I have 5 x $20 dollar bills from 1991 and a $50 dollar bill from 1988.
Any ideas what's wrong with them?
Thank you.

Best answers:

• have you considered using google?
  within 2 seconds i discovered that canadian dollars changed in 2001 therefore there would have been a period after that you could have used them after that they then become worthless, unless you go to the canadian version of the bank of england where they would exchange it.
  exactly the same thing happens in the UK too
  https://en.wikipedia.org/wiki/Banknot..._Canada_Series
• Cheers
  I did use Google and found the same info, but I didn't realise that previous versions of the currency became worthless after being phased out. I do now.
• as i said its exactly the same as the uk.
  try using a 23 year old Ј20 note in the UK and you would have no chance.