Amex Credit Card Complaint

Amex Credit card department,

Billing statement New York

American Express card offered me to shop on - -, 2015, the small business Saturday, and told me if I spend more than $10.00 on -/-/15, I will get $10.00 statement credit, so I did spend $19.00 on a small business - I chatted with Amex rep in earlier -, the rep told me I am definitely qualified. Today I am chatting with a - rep since I received my statement, and the credit is not showing up on statement. Now this rep told me this credit requires vendor approval, and will take up to 90 days to post, the vendor approval and takes 90 days to post were never disclosed in the initial offer. I feel being cheated by Amex.