Restore SSH Access on Ubuntu VPS

I need help restoring SSH access on my Ubuntu VPS. Currently, I can only access the server via the rescue mode provided by Contabo, but not through SSH.

Requirements:
- Diagnose and fix network connectivity issues.
- Ensure server is reachable via its public IP.
- Restore SSH access.

I can access SSH configuration files from rescue mode.

Ideal Skills and Experience:
- Strong experience with Ubuntu Linux and VPS management.
- Expertise in network configuration and troubleshooting.
- Familiarity with SSH and rescue mode operations.

Please provide a brief outline of your approach and estimated time to complete.