Previous resident denied disconnect - how long will this take to resolve?

We bought a house and close on 5/17. I created an Xfinity account for internet services with a requested start date of 5/18. I just received a call that the current (soon to be previous) resident has denied the disconnection of their services multiple times, even though I specifically requested that our service not start until after we take possession. I am not blaming Xfinity for this - I understand it is in no way their fault, it is the previous owner being difficult. 

However, that aside, the person I spoke with also stated that our service is to start on 5/23, which does not work for us. It is not what I requested and I have no idea why it’s been moved with no notice. I work from home and have to have internet. 

So, we now have to take proof of residency documents to an Xfinity store to have the previous owner’s service forcibly disconnected and have ours turned on. My question is: how long will that take to process? Is it more or less immediate?