Can not change my autopay due date

Hello!

I am a newer customer, and I've tried multiple ways to change my autopay bill due date. When I attempt to do it online, the page gives me an error and says it needs to reload. I've tried multiple  ways to access this page, different web browsers, my laptop, my phone, on wifi, off wifi. I can't access the page at all. I talked to a representative through chat who said they changed it but it wasn't. I talked to someone through the phone, they said they couldn't change it and that I needed to go into a store. I went into a store, and the employee said I had to talk to someone through customer service. I explained I was to told to come into the store and they told me to just reiterate that the store didn't do that. I'm a bit frustrated because all I want to due is change my due date but there have been many hoops doing so, all my because the website doesn't work for me for whatever reason.