Overcharged for an online payment

[a1betpr]

Anyone else ever experience this?  I owed something like $1,700 as a final payment that is due in a couple of weeks, clicked through to pay that amount, then a minute later the cruise balance showed as -$2,200 because NCL actually charged my card $3,900.  I didn't even type any numbers in - I just clicked the bubble that said "pay remaining amount of $1,700" or something along those lines.  Of course they told me via online chat that it will be refunded back to the card within 15 business days, but i'm not holding my breath.  I am tempted to dispute the charge with AMEX but I doubt I could get it taken care of fast enough to also make sure the final payment is made in time.  In any case this seems like shenanigans of a whole other level for NCL.