No data/4G in Germany at all

[#1]

Hi, I just arrived in Germany on my first stage of a European trip (France and Spain afterwards). I didn't bother packing my satnav as I was simply going to use google maps or another app. Then the joy when I get off the tunnel and I have ZERO data. Luckily I had a road map, but it made for a stressful drive. I AM able to make phone calls, but I cannot google anything/use WhatsApp/use apps etc. 

It leaves me really quite helpless as I want to google hikes in the area/look up nearby restaurants etc.

I have now spent money on another satnav, with mine being in a drawer at home.

Feeling extremely frustrated. How can I resolve this?

Thanks for your help.

[#2]

@alexad 

Have you tried connecting to a different local mobile network?

[#3]

Yes, it gives me three options: Vodaphone, O2, Telekom. Only with O2 do I at least get bars, so that I can make phone calls. The other ones: zero signal.