Shocking accounts department

My partner has both mine and his cell phone contracts in his name. We have been struggling with our service being suspended almost every month because they say that we have not paid for March and April. Our payment is on a scheduled payment and goes off every single month, our bank statements prove that we did pay for those months. When we ask what caused the issue they said that they changed accounting packages that lead to reference numbers changing, this happened without our knowledge so we continued to pay using the same reference number. It is not our fault that they did not inform their costumers that things have changed. They are demanding that we pay for those two months to reactivate our account even though we have proof that we did pay them, We have been going around in circles for months, i keep phoning in and sending through proof of payment just to have it suspended again the very next month because there is never proof of any statements being logged their system. It just ridiculous that it just continues like this. Once this they have fixed this issue I will be canceling my account and moving to another service provider.