I filed for SS at a local office when turned 65, but was denied as the clerk was unaware that my 20+ years of work in Canada can be added to my 6 US credits. I filed an appeal online, but was ignored even though I got a confirmation that it was received. Then I sent another appeal with all the paperwork to a PO Box in Maryland. Once again, no reply. It has been 3 years since I was supposed to get my SS. How can I get them to reply and process my payments? The phone contact is beyond dysfunctional.
When you say that you were denied, I assume you mean that you filed a claim for benefits and received a formal disallowance letter from Social Security. As long as you filed a formal appeal request within 60 days from the date of your disallowance letter Social Security is required to make a determination on your appeal. However, if it's been 3 years since you filed your appeal then something must have gone wrong. Reconsideration (i.e. the first appeal step) determinations rarely take longer than a year, so my guess is that your appeal request has either fallen through the cracks or your appeal was denied and you didn't receive the notice.
At this point I'd say you have 2 choices. You could either keep pursuing your appeal, which would involve contacting Social Security and submitting documentation of the fact that you filed a timely appeal request, or you could abandon your appeal request and reapply for benefits. The downside of filing a new application is that you could then only claim benefits retroactively for a maximum of 6 months from the date of your new application.
Regardless of what you choose to do, I would suggest appearing in person at your nearest Social Security office if at all possible. You can make an appointment in advance if you can get through to them by phone. If you intend to pursue your appeal, be sure to take documentation of the fact that you previously filed a timely appeal with you when you go. The confirmation number that you received in response to your online appeal request should suffice.