WiFi continues to use DHCP info from old router

I recently had to replace the router in my home. The new router uses a different subnet but otherwise I set up the SSID & password to match. Most of the devices in the house have been able to connect to the new router with no issues. In fact, this phone did so initially. However, at some point it reverted to using the IPs provided by the previous router (DHCP assigned address, gateway) rather than what would be provided by the new router (it is obvious because of the different subnet).

On one other phone that exhibited the same issue connecting to the new router (i.e. using the old IP addresses; I cannot say for certain whether is never connected or did connect and then reverted), I was able to forget the network a few times and then it got the correct IP addresses. My phone does not seem to recover after many join/forget cycles.

Has anyone encountered anything similar? Is there a WiFi cache somewhere that I can clear to resolve this? Any other ideas?

Thanks!

.Tim