Increase in Billing

Go into Cost Explorer in the console and have a look what you're being charged for. You can break things down by service and region etc.

Once you have identified the services that you are being charged for as suggested above, kindly go to the respective service and simply delete/terminate the resources to stop being charged

Try using AWS Cost Explorer (https://aws.amazon.com/aws-cost-management/aws-cost-explorer/) to see the details of your charges. Cost Explorer is free when you use the console with out of the box settings the only billable features are hourly & resource granularity & direct API requests.

Initially Cost Explorer will group the costs by Service, making it easy to see which service is responsible for the cost. You can also switch the Group By dimension to Usage Type, which will show you the next level of detail: the specific units by which your charges are being metered.

Some examples of items that you might find:

EBS:SnapshotUsage - EBS Snapshots that need to be deleted
ElasticIP:IdleAddress - unused elastic IPs

Once you identify the specific usage, you can go into the appropriate section of the service console and remove those resources (delete EBS snapshots, release Elastic IPs, etc).