I think you are mixing up the numbers:

• 0.37GB = the amount of bandwidth you have actually used this month via your Wordpress Droplet
• 356GB = the amount of bandwidth you COULD HAVE used this month without going over your limit and getting charged.
• 713GB = If you don’t create or destroy any Droplets, this is the amount of bandwidth you can use through all of June without going over your limit and getting charged.

The second number (356GB) will increase every day because it is like an allowance. Here are more details: https://www.digitalocean.com/docs/accounts/billing/bandwidth/#monthly-allowance