Unexpected $102.78 invoice this month on Monthly Professional plan — only 1 seat is assigned

I’m currently on a monthly Professional plan.

For the previous months, my monthly payment was around $23.60. However, this month I received an invoice for $102.78.

I checked my Admin → People page and found:

• Full seats purchased: 3
• Assigned: 1
• Available: 2
• I am the only person currently using the Full seat.

My September invoice shows:

• Monthly costs — 3 Full seats: $60.00
• Billing adjustment / Seat updates: $27.10
• Taxes: $15.68
• Total amount due: $102.78

I don't understand why this month's invoice increased significantly when I have only 1 assigned Full seat.

I also checked Billing → Overview, and it currently shows my next monthly invoice as $20.00.

Could you please clarify:

1. Why was I charged $102.78 this month?
2. What exactly is the $27.10 “Seat updates” billing adjustment?
3. Why were 3 Full seats included in this month's invoice when only 1 is assigned?
4. Since I am on a monthly plan, will the 2 unused seats automatically stop renewing?
5. Is this invoice eligible for any refund, credit, or adjustment, particularly for the unused seats or the $27.10 adjustment?
6. If the charge is correct, could you please explain how the $102.78 was calculated?

Thank you.