I'm not sure.
Here are some configuration examples for some ISPs.
They use ipv6 'auto' and then do the configuration on the wan6 interface.
What prefix length does your isp provide?
Are sure 60 will work?
Maybe OpenWRT will fallback to a different prefix length but I'm also not sure about this one.
So you already tried the following config and it didn't work?
config interface 'wan'
...........
option ipv6 '1'
...........
config interface 'wan6'
.........
option ifname '@wan'
option proto 'dhcpv6'
option reqaddress 'try'
option reqprefix 'auto'
..........
config interface 'lan'
.......
option ip6assign '64'
..........
And remove the route6 config section.
Then reboot the device.
The odhcp6c command line looks fine to me.
Latest trunk or latest stable version?
Do you have banip, bcp38 or similar packages installed?