No response from seller and item not ever shipped but was paid for

[jerfor-94]

What do you do if a seller doesn't ship your item and does not respond to any of your contacts the product is not due to arrive till Tuesday but still has not been shipped out so there's no way possible that this item can arrive on time and I have been reading now that I have purchased this item and the seller has had nothing but complaints about items not being shipped on time or contacting customers back all this month what should I do