IPv4 to IPv6 changes

As a residential customer, I have a computer that I could sign into from the public side of my Linksys WiFi router. However, a few days ago, Comcast changed my public IP address from IPv4 to IPv6. Everything is working except my ability to access my LAN from the public side of my router. Linksys says I need some information that only Comcast can provide, but technical support keeps blaming my Motorola Surfboard modem, which I believe is wrong. Here's what I need, according to Linksys:

1) Network setup prefix:

2) Prefix length:

3) Border relay: (I'm thinking it's an address)

4) IPv4 address mask length: