Cox says I have used 75% of my data in 20 days

I recently received a text alert saying I have used 75% of my data usage for this billing period which is 1.2 Tbyes total. I myself have temporarily moved to Jax, Florida. I have Xfinity internet service but use my Dads Cox login to watch HBO, ESPN, etc.

My question is this, Does my data allowance for the month get used if you are streaming cox services on another providers internet service?
I have unlimited data internet with Xfinity BTW. If thats not the case could my Dad streaming shows through a Roku box use that much Data?

Thanks!