Hi Eduardo,
Take a look at Whatsapp propaganda research
by Soma Basu, and also by Kiran Garimella +co-authors. BJP public groups have location
names eg BJP4Orissa, BJP4UP etc and whatsapp group data collected by
researchers can throw up relative extent and intensity of propaganda. There are also circuitous ways to trace location from phone numbers from whatsapp groups used in research but I do not have details. There is limitation to availability of data for only public groups.
You may collect whatsapp data for upcoming elections by joining public groups as these researchers did.
Granular data is there only for a week so for 2019 polls, it may not be there now except in aggregated form. You could start now for UP polls and see details available(and not available) for location. I had old data from 2019 downloaded then, but need to locate it back again. FB data also has its own disclaimers and limitations.
Hope that helps!