I use a pressure washer to make cuts in the soil when in the neighborhood of where I suspect there are pipes or wires. My soil is too variable to reliably "feel" things. I'm sure that others are more talented.
It's 2 companies and neither seems to know what's going on. To complicate things I don't have an address yet and the utility didn't provide any contact information when they marked the line. I suppose if I get frustrated enough cutting the line would get some action.
To the OP,
@homedad, I would talk to Frontier and Verizon some more, as if they have to touch the wires and resplice, it often is not cheap, and even pricier if it is an emergency.
For the liability coverage alone, I would be really, really tempted to hire a contractor to do the work for me as they may have access to better maps or know the local history better with the underground cables in the area, and if not they have insurance that's going to be better than mine for this. Some times, it is money well spent to let someone else do the work.
In my book, since this could get expensive, potentially all on your nickel, I would be super nice, make appointments, go see folks in charge with photos and GPS coordinates and find out the costs before touching the soil. Ideally, you can convince them that you will be a long term, valued customer, but that's not always possible. I've lived places with huge copper and monster fiber cables that weren't local. Breaking one of them is pricey. (I watched the power company score a direct hit on a 10,000 pair underground copper telco cable once. Yes, "mega" pricey. 24x7 work by two telco techs in a 6x8x8 excavation and who knows how many techs running around town injecting signals. It took a week plus to do, IIRC)
I would also point out the possibility that the cable might be neither Frontier nor Verizon. Just because it is labeled "telco" for 811, doesn't mean it has to be them. I know that there are big fiberoptic cables in our road that don't belong to any of the local Telcos, and, interestingly enough, not on their burial maps (which I have seen). The older linesmen know that the cables are there only because they have seen the fiber access points, but that wouldn't necessarily be true of an outsider or new tech...crazy.
Good luck!
All the best,
Peter