If you have been blacklisted by a different vendor with this email address, this may be why. The way the blacklisting works is each vendor can set a certain threshold. If a buyer has been blacklisted by for example 3 vendors (many vendors will automatically add buyers to the blacklist if they request a refund), then any other vendor who has set a threshold of 3 will have automatically blocked that buyer as well.
With a threshold of 4, 4 vendors will have had to blacklist a buyer, etc. This is the most likely cause of why you have not been blocked specifically by a particular vendor you were trying to buy from.