Migration from asus RT-N66U to RT-AC88U Plusnet username and password not recognised

Hi All.

I have decided to upgrade my asus RT-N66U that has been running on Plusnet for a couple of years and have bought an Asus RT-AC88U.

I get an error username and password are not correct for the internet connection.

I compared the WAN config and Username and password settings in the configs between the routers untill I am crosseyed and cannot see any errors and even got my wife to check as I did not trust myself.

Any Advice would be appreciated.

Thanks

Paul