Can I use the same bitcoin address to receive more than one payment?
An old address can be reused, but its usually recommended you don't do so for privacy reasons. 

Even if you wallet is displaying a new address, it should still show a balance that includes any recent payments made to older addresses. 

To be sure, check the receiving address on a block explorer website, and if the vendor is telling the truth, you should see the recent payment in addition to any past transactions. At that point,  try re-syncing your wallet if the payment isn't displaying properly.