So furious with Amex I am likely dumping them before next renewal bill comes due

I got my 1st Green car way back in 1988, I have had a Platinum card for the last 5 years, been traveling quite a bit and the benefits have been useful. I have never once been late and always pay my balance in full. Last billing statement when making my payment I think my connection dropped before the payment was finalized, I did't realize, and was blissfully ignorant, I generally make my payment 1-2 weeks before the due date, and was a bit shocked when the $29 late fee showed up, I immediately payed and reminded myself to pay better attention in the future. Fast forward to this months statement and I have a $135 interest payment due! I contacted customer support and was informed I was on the hook for the late fee AND 2 months of interest, has anyone heard of this before? I think it was 1 or 2 days late.