I am an American citizen, I moved to Canada when I left the US Air Force. I retired at 67 and applied for my Social Security benefits. I also qualified and paid into Canada's Old Age Pension and receive a pension. The US steals half the pension in a clawback that I and my employers paid into to qualify. Is there any way to regain a full pension from America?
Probably not. It sounds like your U.S. Social Security retirement benefit is being reduced due to the Windfall Elimination Provision (WEP), which results in the use of a less generous benefit calculation formula for people who receive pensions based on their work that was exempt from U.S. Social Security taxes. If you were only eligible for the Canadian Old Age Security Program (OAS), then WEP wouldn't apply to your U.S. Social Security benefits. However, WEP would likely apply if you worked in Canada and also receive a pension under either the Canadian Pension Plan (CPP) or Quebec Pension Plan (QPP).
There are exceptions to WEP, which are listed in the following Social Security publication: https://www.ssa.gov/pubs/EN-05-10045.pdf. The most common exceptions that might apply in your case are a) if you had more than 20 years of substantial earnings in the U.S., or b) if your U.S. Social Security credits were used by Canada in order to make you eligible for your CPP or QPP pension.
If you think that you may meet an exception to WEP or that WEP is erroneously being applied in your case, you should contact Social Security and file an appeal or ask for review of your case.