Sudden increase in charges for Elastic Compute Cloud

To review your costs and locate which services are costing more, you will need to use cost explorer https://docs.aws.amazon.com/cost-management/latest/userguide/ce-what-is.html

If you wish to be alerted on costs through the month you are best to setup budget alerts https://docs.aws.amazon.com/cost-management/latest/userguide/budgets-managing-costs.html

As for a refund, if these are legitimate costs incurred by yourself then I don’t believe you will be able to receive one. However any billing issues you can contact bill support in the account by raising a ticket https://docs.aws.amazon.com/cur/latest/userguide/billing-get-answers.html

You will need to review the costs and which service increased and locate why. It may be down to traffic,CPU, storage, end of free tier etc

1. Go to Cost Explorer -> Choose Date Range in right pane
2. Granularity -> Daily
3. Dimension -> Usage Type
4. Service -> EC2

Note: Repeat same by changing option in Dimensions field as Region, Cost Category and Availability zone, Cost Category one by one.

This would show you when and what are the resources/which region/AZ that's happening.

If you want to setup alert, you can consider setting up AWS budgets and configure alarm on those, which would notify you, if you cross the defined usage threshold. Follow the Well Architected Lab instructions here for setting up budget alert based on your usage.

As mentioned here in previous answer, contact AWS billing support and brief your situation, based on that it'd be decided whether it can qualify for refund or not. But I would strongly recommend to setup AWS budget alert. Be noted that budgets are not real time and there may be lag of 4-6 hours but you can definitely avoid such surprises if some of resources left turned on accidently/unknowingly.