What’s not to believe? You’ve had tests done. I was diagnosed with AS from a simple X-ray. You’ve had a MRI. MRI would detect inflammation even BEFORE actual damage to the joints. Your doctor would have seen inflammation. Not "maybe". Absolutely.
AS is very easy to diagnose once you actually do the tests. If doctors say you don’t have AS after doing an MRI then you don’t have AS. You just don’t.
Be happy you’re clear of this disease and wipe it from your mind.