bought 5 domains - DNS for one just will not resolve

• PROBLEM - I bought 5 domains - the most important of which refuses to work after over a week of tinkering, I tried two more, both work flawlessly with changes I make taking effect almost instantly
• HINT? - problem likely stems from my putting the internal IP of the target rather than the Public while initially setting it up
• DETAILS - I am creating 2 A-Records, a www. and a blank field (domain only), just as with the other domains. These are the only records, no changes to others (except as troubleshooting below: pings don't resolve, browsers report 'address not found' from multiple networks, nslookup gives a 'SERVFAIL'; pings don't resolve from the target EC2 either (to the issue domain name). The hosted zone is Public, the record test function returns 'no issue'.
• TROUBLESHOOTING :

1. changed the A-Records to the public IP
2. waited 1-2 days
3. removed the A-Records and added new ones with Public IP
4. waited
5. Read through the Route 53 docs - nothing seems to pertain to my situation that I haven't already tried7
6. eventually totally removed the hosted zone
7. waited
8. added a new hosted zone file with new records
9. waited
10. Updated the SOA & NS server/text to that from the working hosted zones
11. waited

I'm at the end of my rope on this... any thoughts on how to fix this? thanks