Hey MM what plan are you on for data...I just looked on Telus's web site and to my amazement...
"Additional usage will be charged at $0.05/MB. Cannot combine with any other data plan.
Tethering included. Additional data is charged by the MB or GB and is rounded up to the closest KB (1 GB =1,024 MB; 1 MB = 1,024 KB). Data usage is subject to a monthly overage limit of 10 GB."
I assume you are on the Diamond 15 Unlimited Data Plan but I dont know if this would apply to grandfathered plans or not but maybe you could get some of that cash back.
I also looked on my contract and now where does it state that use of Tethering is either excluded or included...who knows. Good Luck.