RSAWEB PAYMENT INVOICE RECEIVED WHICH STATE PAYMENT WASN'T MADE ONE YEAR LATER

My girlfriend has been Using this Internet provider for a couple of years made all her payments on time every month. So last month out of the blue she was told that a payment wasn't received of the month of April of 2024 that a full year later and that seems impossible not to notice as soon as x payment was missed right we have all the proof of payments but yet the feel like we should pay the full amount again which is not even our mistake that it wasn't loaded on their side I just want to know what the steps that we can take for this unprofessional services provided by them trying to make their mistakes ours