You’ve been charged $300 for a payment to Envato, without your knowledge? Sorry to hear that. You really need to contact Paypal though, rather than Envato.
By all means, speak to Envato support, as they may be able to help with any investigation, but the only way that Envato could have processed the payment is if somebody has specifically requested for a payment to be made… and if that wasn’t you, then somebody has access to your Paypal details, which needs to be reported to Paypal asap. I’d also recommend you change your Paypal and email passwords as soon as you can.
To raise the issue with Paypal, log into your account and go to ‘Tools’… ‘Resolution Center’… and then ‘Report a Problem’.
And here’s the link to open a ticket with Envato…
https://help.market.envato.com/hc/en-us/requests/new?ticket_form_id=37840
Hope you manage to get it sorted.