"20 days" information comes from here:
TELUS
about TELUS
terms and conditions
shipping, delivery and return policy
http://about.telus.com/legal/ship_return.html
"Legal" means legal.
So pack everything up (check the site above for things they want), take pictures of everything you packed, make copies of any papers, and send it back via private courier such as FedEx with good insurance (for the full price of the phone).
Enclose a letter stating that
"I have purchased the phone on such and such date, don't like the phone, and would like to return it according to Telus Return Policy set forth at http://about.telus.com/legal/ship_return.html" (enclose a copy with relevant paragraph highlighted).
Make a copy of all this as well.
Track the package, and the day after they have received it give them a call
"to get a different phone instead of the one I returned to you (that you received yesterday)".
Note that most carriers permit such returns only once, so if you have returned another phone within last 20 days, they may indeed refuse this return.