Questions about networks and routing of wan packets. IP spoofing. UDP?

Question

Computer networks

I can not get through to any machine of normal users in any way.
I asked them to turn off the firewalls, everything that is.
No machine responded to the ping, the udp packet did not respond with "Destination is unreachable".
I looked at everything in wireshark. Packets were sent both through python and through netcat.
In short 0 reaction. However, when I get pinged, my machine responds fully.
And now the questions:
How do mobile networks work, and how is communication with a user on a modem and cable practically different? The same question is about users of wifi networks, whose router is eventually connected to the cable. What prevents packets from reaching the target machine, except as a firewall?
Does ip spoofing work in 2019? If I specify someone else's ip in the udp header of the Source packet, will the packet survive? In my case, the packet simply did not go when I specified the ip of a friend's network.
If there is a person who can help figure it out and knock his machine with wireshark enabled, then I will be very happy
UDP: Everything is still like this, machines 0 reactions, HOWEVER. If you ping and wait a minute, for some reason, answers begin to come after hundreds of pings (for new pings, not for 100 old ones).
In general, nonsense, given that the machine does not respond to everything else

Answer 1

1) are you pinging with the right utility, because ping natively is not udp, but icmp packets, but some unix machines use udp for ping.
2) regarding the difference in wireless networks, there are differences at the level of packet transmission, mobile networks have more,
wi-fi has less. A broad question indeed. There is no difference at the ip level (OSI level 3).
3) It works, but there are mechanisms for suppressing such packets, sometimes enabled, sometimes not.
In general, to better understand the situation, it would be nice to understand the scheme of what you want to do.
Wireshark log, traceroute output. endpoint ip addresses