The billing date is the 5th, and the billing period is from the 6th of each month to the 5th of the next month.

Consumption on January 28 will be counted as the account period from January 6 to February 5, and the latest repayment date is February 28 (?, February does not have a 30th day).

What do you mean by repaying the full amount in January?

The simplest thing is to look at the bill on February 5th. It shows how much you should pay back at the end of the month.