Hotspot allowance is used up in 2 days

[Kellyandthedogs]

The last few months, I’ve been getting a message early in my billing cycle that I’ve used up my 15 GB high speed allowance for the month. I have not changed my usage pattern so why is this happening ?

I got the same message today, just 3 days into my billing cycle. It would be impossible to use that much in 3 days! 
Could someone else be tapping into my account??  
I’ve had lengthy conversations with Support to no avail.