Didn't get the promotional credits as described

Your agent tricked me into signing up for the next service level on my complaint call for slow service. That's a new topic for later. But part of what he stated was that I'd get a $100 promotional credit for 12 months of the upgraded service.  My first credit was only 6.45 due to the partial month. One would expect if you give credits for a partial month at the beginning, you must also give partial credits at the end of the promotion. So the final month should have included a $93.55 promotional credit in order for me to get the $1200 I was led to believe I would get against my bill.  But that final partial month ignored my remaining credit and I did not get the last $93.55 that anyone would have expected to get.  This strikes me as very shady.  If you're going to issue only 12 credits, anyone would have started the upgrade a few days later to get $1200 instead of $1143.55 wouldn't they?  No, because your agent didn't explain the promotion carefully or clearly.  He was just trying to make a commission and didn't care if I was cheated or not.  I want $93.55 from my last CC charge refunded to my card.  That's only fair.