HA instance without access after changing ISP (internet service provider)

Good morning,
I hope everything is fine with everyone!

I have been using HA since last year.
I use an RPI4 with the 'Home Assistant Operating System' installed directly on the SDCard.
I have local access through the browser pointing to Local IP (http: // ip-local: 8123 /) and remote access using Nabu Casa.
This week I changed my internet provider (ISP) and lost access to HA, either local or remote.

Before making the exchange I did the following procedures:
- Configured the fixed IP of the HA on the new router (linking to the MAC);
- Adjusted the 'Internal URL' for the new local IP (changed from 192.168.0.X to 192.168.15.X);
- Configured Port Forwarding (8123 for Local IP) on the new router;
- From the HA user interface, I changed the network settings (Static IP) for the new provider:
    - Local IP: 192.168.15.X (IP reserved for my HA);
    - Default Gateway: (router IP);
    - Primary and Secondary DNS: I changed to the provider's DNS (ie, I did NOT use Google and

Than I disconnected the old router, plugged the RPI/HA network cable into the new router, energized and ........ lost the connection. I've already booted but I can't access my HA instance - neither by the local IP nor by Nabu Casa.

I'm afraid I have to redo the ALL installation and configuration process from scratch again (but I have snapshots backups).

Did I falter at some step?
Is it possible to get around, since I am without access to the instance?
Should I have maintained Google's DNS or has nothing to do with it?

If you can help me, I will be very grateful, as it took months and many hours to keep it running just as it was and I would not like to have to do it all again.

Thanks for listening!

Tomas Teixeira
[email protected]