Why am I getting charged for a stopped instance? and charge is still increasing.

Current month costs is what you have already incurred from the 1st day of the month until now (the 20th day of the month).

Forecasted month end costs is what you are predicted to have incurred from the 1st day of the month to the last day of the month (all 31 days).

You can read it as saying that you have incurred 25c of costs from 1st to 19th, and AWS is predicting that - based on your current usage - you will be incur 0c of costs for the 20th to 31st. Giving a total of 25c for the month.

It's just a prediction, not a hard-and-fast invoice. if you provision more instances and make use of more services between now and the 31st then these may increase the bill at the end of the month.

Your Amazon EC2 usage is calculated by either the hour or the second based on the size of the instance, operating system, and the AWS Region where the instances are launched. Pricing is per instance-hour consumed for each instance, from the time an instance is launched until it's terminated or stopped.

Refer to https://repost.aws/knowledge-center/ec2-instance-hour-billing how EC2 is billed.