VPS Accessible only through Serial Console

I have a VPS (with AphaVPS) that is running Ubuntu 18.04. Since a couple of days, I cannot reach anymore the VPS through SSH.
I managed to connect using the browser serial console provided by AlphaVPS and from inside the VPS I cannot ping anything. I spoke with the customer support of the provider and they say that everything is completely fine on their side. What could be the issue then? Before this happened I didn't make any configuration changes, nor installed any new package nor anything.