"I recently sold my first item on eBay"

And as you're a new, inexperienced seller, hopefully your US buyer is honest  as you could lose your money and your item if they file a MBG dispute.

Not that it always makes a difference   but what  is your buyer's feedback like ?

Are they experienced or new ?

Sorry, I should have also added that if you still wish to interact with an eBay agent, all you need to do is tell the bot "speak with agent" and follow the prompts... although you have to do so during their operating hours or you'll end up with the following message... 

No there is no phone number.

Yes there are tariffs payable for US sales, although eBay do not calculate or collect said tariffs. So there is no point in contacting them anyway.

The tariffs are entirely your responsibility... whether you cover it yourself or pass it on to the buyer is your call... but unless you have a Zonos account, they have to be paid at the point of lodgement with AP. 

Alternatively, if you don't want to pay the tariffs, you can use a courier such as DHL (as an example) who will collect any amount payable from the recipient.