I’d do a bit more sleuthing to try and discover why your usage jumped so much. A nearly 300 fold increase in usage should be investigated.
Start by changing your Wi-Fi password, and looking at traffic patterns in the Admin panels of your router.
I have a similar problem. I just received my bill and found the Telus is showing 490.90GB used in one day, July 08. I am on an Internet 6 plan, 6MB/S download. I would have had to be maxed out for 23 hours straight to hit this kind of single day usage. My normal usage in less than 10GB per day.
Here is where my story is also the same as yours. During the evening of July 08 I signed up for faster internet and unlimited data, both starting on July 09. So like you, the day before an unlimited data plan kicked in, Telus is claiming I had data usage that my connection could not realistically provide.
I called Telus customer service today and spent 30 minutes with a polite front line agent who was as perplexed as I was about the extraordinary one-day data usage number. Unfortunately the agent could not help me but did put me through to a customer service manager. The manager provided me with a credit for the entire month's data overage (522GB overage). My Internet 6 plan allows 150GB/month but I have been consuming just over 200 GB/month and had expected a $20 overage charge instead of the $45 charge I received. I was pleasantly surprised with how this was handled.