Citibank Credit Card Complaint

Citibank Credit card department,

APR or interest rate Texas

I have had a credit card with CitiBank since -/-/-. Unfortunately, I missed the first payment because I was not accustomed to having another payment, and they raised the interest to the penalty rate 29.99 %. From that point -/-/-, I have had on time payments. They have only reduced my interest rate to 28.74 %. When I questioned them, they said it was their prerogative when to lower it. I thought after 6 months of consecutive on time payments they had to return it back to the pre penalty interest rate? They refuse to talk to me, and only direct me to " send it in writing '' to a generic PO Box address.