BUYER PROBLEMS:

No invoice. 
No seller response to inquires/questions submitted through Ask the Seller.
No response to requests for new invoice.
No notice of auction shipment.
No acknowledge of paypal payment.

POSSIBLE SOLUTIONS:

First off, before you become frustrated and fire off yet another email to the seller, check your Spam Mail, as for some unknown reason, ebay mail and paypal mail and mail sent through ebay questions will on occasion be eaten, so to speak, by spam filters. 

If you need an invoice, go to your items won in ebay and click on the pay now button.  This will bring up the invoice.  There is a link at the bottom of this invoice/payment screen for asking the seller questions.  Using the pay now button does not require a payment so this screen can be used to talk to the seller.  It can also be used to make payment by all method types accepted by the seller and it will list the types at the bottom of the screen.

If you still do not get a response, check the listing for a phone number for calling the seller.  IF, AND ONLY IF, YOU PURCHASED OR SOLD AN ITEM, ebay will provide a phone number for buyer and seller after ebay verifies that the transaction was completed.  Go to ebay site map, A-Z list, and check under CONTACT SELLER for the link to click to let ebay know that you need this information.  Have the auction number ready as ebay will require this information.  After ebay verifies the transaction was completed, both buyer and seller will receive contact information through email address listed with ebay. Again, check spam filter if you don't get it within the listed timeframe ebay provides. 

Communication is the key to all successful transactions but sometimes you need a little help finding it.