Questions about $100 deposit and apparent overcharge after adding stream bundle

I was paying $50 a month for internet service in August 2026.

In September of 2026 I added a $35 streaming bundle including the "free" streaming (xumo) box.

My September bill, paid in October, was $150.

My October bill, paid in Nov was $112.98.

My Nov bill, to be paid in Dec, is $85.00, which I would have expected my Sept and Oct bills to be.

I chatted with an agent in September about this and they assured me it would all work itself out.

After thinking about it, I wasn't satisfied with the chat agents explanation so I went into my local Xfinity store. After looking at my account in detail, they said I was going to pay $27.98 on Nov 1. They were only off by $85.

I have 2 questions:

1. Apparently the $150 Sep 2026 bill included a $100 deposit. Can you explain this "deposit" to me? Please?

2. Why is there an additional $27.98 on my Oct bill?