Have you read the chapter about the USART in the datasheet? It takes a few tries for it all to sink in, usually.

If you're reading zeros, that means it's either empty, or it actually thinks a zero was received.

Depending on how you've structured your code, you may consider turning OFF the USART while you look for the break.

Once you've found the break signal, turn on the USART and clear it a few times, just to make sure it's ready for whatever data you're hoping to capture.

JEC