The one & two year plans are prepaid, so if you upgrade from one to the other, you'd be charged the difference--but would also save the difference between the two.
$7.95 x 12 = $95.40, so owing $71.40 means they switched you two the two-year pricing, but gave you full credit for your 1-year prepayment.
Where that money comes from would depend on if you have any rewards built up & how your billing is setup. If you have rewards from referring people, I believe they will automatically pull it from there first.
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