the fact that a VPN worked, indicates that your IP address was being blocked by the website. That means it's really not a Cox issue, but a problem that your credit union has to get resolved by their web site host.
I’m certain it’s an sdccu issue. However, speaking to someone to get it resolved is where I’m coming up short. They assured me they spoke to their IT dept but the gatekeepers won’t let me through to speak to someone to confirm or who can actually help.
I know what it's like. I used to work for Cox, AND Previous, worked for a data processor that handled Credit Unions over several states. SO.. I REALLY DO know both sides of the issue. I certainly understand your frustration, and hopefully someone at the credit union is doing something. I would like to think so, since most people at credit unions are really decent people, and they care about their members.