I am 74 years old and have been receiving Social Security since I was 65 (some 9 years), and also a Canadian Pension, because I have dual citizenship, born in the U.S. The Social Security Office contacted me by letter just yesterday saying they were reducing my U.S. Social Security by $267 monthly. That action left me with only $39 U.S. dollars this month, since they decided to reduce my $838 monthly benefit retroactively starting March 2019. They tell me that I will receive $571 on August 3, 2019, and that this same amount will be ongoing after that. They stated their reason is that I fall under the Windfall Provision. I work and paid Social Security since I was a sophomore in high school in the U.S., some 25 years; moved to Canada and worked there some 27 years. I ask for your help in how to appeal their decision. I have to send the appeal form very soon and I don't know where else to turn. I am sincerely grateful for any advice your have in your area of expertise.
You should receive a formal notice about Social Security's determination to reduce your benefit rate in the mail, and that notice will explain your appeal rights. The first appeals step is called reconsideration, and you can request reconsideration by completing and submitting a form SSA-561(https://www.ssa.gov/forms/ssa-561.pdf) to Social Security.
However, based on your description it sounds like your U.S. Social Security retirement benefit rate probably should be reduced due to the Windfall Elimination Provision (WEP). The WEP provision requires the use of a different, less generous, benefit computation formula when calculating U.S. Social Security retirement benefit rates for people who receive a pension based on their work and earnings that weren't subject to U.S. Social Security benefits. Since your Canadian pension is based on earnings on which you didn't pay U.S. Social Security taxes, you would be subject to a WEP reduction unless you meet an exception to WEP. The various WEP exceptions are outlined in the following Social Security publication: https://www.ssa.gov/pubs/EN-05-10045.pdf.
You don't say when you started receiving your Canadian pension, but I assume you must not have started drawing it until March 2019 if that's when Social Security says that the reduction in your U.S. benefit rate becomes effective. If you've been receiving the Canadian pension longer than that, then the WEP reduction likely should have been applied to your U.S. benefit rate even sooner.