New line Installation

I recently moved into a house where the landlord has their own Xfinity Account, but It's not as fast (or as close to me) as I would like. I was under the impression that using a cable splitter and having both boxes connected to the same source would be fine, but I was mistaken. I am wondering how I would go about getting another line installed. Sadly, I have already created an xfinity account, received my gateway, and my first bill is rapidly approaching; meanwhile, I cannot access the internet I am about to be paying for.