Can't ping my Fritzbox 7490 from the internet

Hi,

I can't ping my Fritzbox 7490 from the internet. Should I be able to? Just results in no response if ipv4 address pinged from phone (on cell connection) or one of those online ping utilities.

I've checked, Stealth mode if disable on the Fritzbox.

The bigger problem is that my RDP connection to a PC fro the internet stopped working. I tried heaps of things to diagnose it, and in the process discovered I couldn't ping the router. Tried calling 2Deg tech support, but on hold for an hour so gave up.

Things I've tried to fix RDP:

-Can RDP to PC from within LAN

-Can http to web server on same PC from within LAN

-Setup up port forwarding a few times. Actually reset Fritzbox factory settings, to start from scratch, but no luck.

-Tried RDPing to internet ip address, instead of DynDNS address, but same result

Any ideas what to check for next?

Thanks!