Utility Bills Are Confusing

I've been paying the utilities at my rental house. My original idea was to make it a short-term furnished rental. The current residents want to stay until January and longer if I let them. They wanted to put the utilities in their name so that they didn't need my permission when they wanted to change services or if they had a problem and had to call customer service. I said ok and the switch began. Now I have to figure out how much to charge them for half of a month.

Some of the bills were on automatic bill pay but others, like the water bill, I usually paid $200 at a time so that I only had to pay the bill every 6 months. So, some bills had positive balances and some negative. The cable bill was one of those auto-pay bills but when I got the last bill it said -$36.00. I thought that was odd since I had just paid a big bill but I wrote the check and I was just about to mail it when I decided to look at the bill again. Last month I owed $96.00. This month -$36.00. Hmmm, I think that negative means they owe me! That makes more sense. I was wondering why it was so expensive. I think I'll call them just to make sure. Now I just have to gently peal off the stamp so I don't waste it.