There should be no reason to change your Sonos Account/credentials and I will assume you have not factory reset your Sonos product(s), as there’s no good reason to do that either.

I assume IMZEE is your new routers WiFi SSID?

First of all, ensure your mobile device/operating system meets the system requirements mentioned here:

• https://support.sonos.com/s/article/4875

If you are able to wire the Beam (temporarily) to your new router - then try that too and follow the steps mentioned in this link:

• https://support.sonos.com/s/article/1061

If problems still persist after that, check the routers WiFi segments are not isolated from the wired LAN. Also disable ‘Airtime Fairness’ and ‘QoS’ (if those features are available on your router) and then maybe check/change the 2.4Ghz WiFi band to support 802.11 b/g/n compatibility and maybe even try the WiFi ‘security mode’ set to WPA2-AES Personal. 

Reboot the router and see if that may work and that you are able to manage/change the network credentials after making those few changes.