• You ran excessive balances
• You paid via 3rd party checks
• A 3rd party check bounced
• You had excessive disputes
• You had a late payment

Amex deems you to be a huge risk to them and they're not wrong. The disconnect is that you don't feel like you did all these things, your AU did. Even in your OP, you claim to have never made a late payment even though you admitted to it earlier in the post. But of course it was "because of the AU again". I echo the earlier comments: learn from this and move on.