Product: Credit card or prepaid card

I applied for an American Express Blue Cash Credit Card, which promised to the approved applicant, {$300.00} statement credit once I spent {$3000.00} within 6 months. 
I received the card in XXXX and spent the {$3000.00} by XXXX. 
When I called, several times, I was told the first time that they'd look into the promotion and get back to me, which they never did, and second time they told me, after going through 4 different agents, that they disqualified me for the promo. 
I argued that they approved me for the card and they said that they reserve the right to approve me for the card but not for the promo and that I agreed to it - which i did not! 
Even if they did, it'd be misleading and in violation of clear display of all conditions and not mislead and fool customers. 

Here is the language I recorded from the promo at the time. 

{$300.00} Statement Credit To qualify for the {$300.00} statement credit, you must make purchases with your Blue Cash Preferred Card from American Express that total {$3000.00} or more within your first 6 months of Card Membership starting from the date your account is approved. The statement credit will be applied 8-12 weeks after the spend threshold is met. If we in our sole discretion determine that you have engaged in abuse, misuse, or gaming in connection with the welcome offer in any way or that you intend to do so ( for example, if you applied for one or more cards to obtain a welcome offer ( s ) that we did not intend for you ; if you cancel or downgrade your account within 12 months after acquiring it ; or if you cancel or return purchases you made to meet the Threshold Amount ), we may not credit the Statement Credit to, we may freeze the Statement Credit credited to, or we may take away Statement Credit from your account. We may also cancel this Card account and other Card accounts you may have with us. Eligible purchases can be made by the Basic Card Member and any Additional Card Members on a single Card Account. Purchases to meet the spend requirement do NOT include fees or interest charges, cash advances, purchases of traveler 's checks, purchases or reloading of prepaid cards, purchases of gift cards, person-to-person payments, or purchases of any cash equivalents. Additional Card Members on your account are not eligible for this offer. To receive the {$300.00} statement credit, your Card account must not be past due or cancelled at the time the statement credit is posted to your Card account. 

You can earn a {$300.00} statement credit after you spend {$3000.00} or more in eligible purchases on your Card within your first 6 months of Card Membership starting from the date your account is approved. In rare instances, your period to spend {$3000.00} may be shorter than 6 months if there is a delay in receiving your Card. Also, purchases may fall outside of the 6 month period in some cases, such as a delay in merchants submitting transactions to us or if the purchase date differs from the date you made the transaction. ( For example, if you buy goods online, the purchase date may be the date the goods are shipped ). The statement credit will be applied 8-12 weeks after the spend threshold is met.