Hi
If you have an account on ssa.gov you can log in and see if there are perhaps any notifications there for you?
You can also use the chatbot there to request a call back or call the main LOCAL number and then say "Help Desk" when prompted for an extension. That should get you through faster, and requesting a callback that way avoids the hours long wait times that can often occur on their phone system

SSI payments are lower than SSDI and so that may be the reduction reason? It all depends on your situation, and they are the only ones who can provide the details