Enter USA on VWP after B2 overstay?

I have a B1/B2 visa on one of my passports. A few years ago I went to the United States on this visa and ended up overstaying for a few weeks (~20 days). I applied for an extension (form I-539) before the required departure date on my passport entry stamp, but never received a response (and I don't have any proof that the I-539 was sent, neither can I access the website anymore.)
Since then I became a citizen of a country that allows travel on the visa waiver program, and I plan on using that passport. The rules of the VWP say that you can't apply for it if you have violated the VWP rules before. I'm confused since it could be interpreted that I violated the rules of my previous visa by overstaying, but it was not the VWP.
Should I use VWP or try to get a new B2 visa?
Best Answer
As I understand it you timely filed the I-539, included the filing fee and have no particular reason to think the application wasn't accepted, but left before getting a response. If this is what you are asserting then you have no particular reason to think you did anything wrong and can only be wondering if the US sees this the same way.
If this is the case then the easiest way to find that out might be to apply for an ESTA for the new passport. Answer all the questions accurately, including the one asking about your other passport. If that application succeeds it is a pretty good indication that they are not unhappy with you, if it fails you'll know for sure that you need to pursue a visa.
I think the ESTA application is about the simplest and most authoritative way to get an answer to your question. They will know what happened with the I-539.
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What is a Visa Overstay? Consequences and Solutions to Over staying a Visa
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