Auto pay is on, but charges remain unpaid!

We have Autopay turned on and billing/payment details up to date, and everything was working fine. However, for the past four months or so charges are no longer deducted from our account, but we rather receive past due notices, have to sign in to manually initiate the payment from stored credit card. That's annoying to say the least and clearly not the purpose of autopay, which is supposed to eliminate the need to remember paying the bill and avoiding late fees! Kindly look into what may be causing the issue and fix it (including reimbursement of late fees). Thank you!