Citibank Credit Card Complaint

Citibank Credit card department,

Advertising and marketing Washington

I have a Citi Prestige card with Citibank. Upon calling for retention I was told about an offer on my card if I spent $ - a month for 3 months, Citi would refund back to me $200.00 for that spend. For the next 3 spend cycles I spent $4000.00 a month on my Citi card often using the Citi card when it would have been better to use other credit cards if not for this offer. At the end of 3 months when I asked about my reward Citi basically told me they had defined 3 arbitrary periods a month and my spend doesnt fit the $ - a month as defined by them arbitraririly. I would like to clarify, I was never told about these arbitrary periods in my call to Citi and its impossible to predict that Citi would mess up something so straight forward. I escalated the issue via Citi but today I got a generic letter which tells me I have not met the requirements completely ignoring the nuances of the case.