If you were to share a screen shot of what you are seeing, it would be easier for us to offer comment.
The most likely reason is your billing period is from the 1 April, and the 9 or 10 days in March are prorated for the period between March 1 and March 31. If you were already a Telus Subscriber for other services (home phone, TV, etc) then your internet bill would have the same service intervals as these services, and the few days in March will be prorated for that period.
Remember, this Neighbourhood is inhabited by customers, just like you. We have no insight to Telus business plans, and no connection to the internal workings of Telus. We volunteer to share knowledge about Telus products and services which we have gained by experience or surmise.