Raspbian restart network without reboot

When I am using raspbian with a 4g USB modem, sometimes the network goes down and there is no option to bring back the network unless I reboot the raspbian. In such cases, I try: service networking restart with a cron every hour; this doesn't work. I tried also ifdown -a && ifup -a -- not much better. The thing is, when I execute these commands in a terminal, I get no output. What is the solution to bring network as if I rebooted? root@raspberrypi:/home/pi# ifconfig -a eth0: flags=4163 mtu 1500 inet 192.168.0.100 netmask 255.255.255.0 broadcast 192.168.0.255 inet6 fe80::48f5:e07c:1544:2d24 prefixlen 64 scopeid 0x20 ether b8:27:eb:38:6e:29 txqueuelen 1000 (Ethernet) RX packets 23902 bytes 8949877 (8.5 MiB) RX errors 0 dropped 17 overruns 0 frame 0 TX packets 30039 bytes 6388288 (6.0 MiB) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0 lo: flags=73 mtu 65536 inet 127.0.0.1 netmask 255.0.0.0 inet6 ::1 prefixlen 128 scopeid 0x10 loop txqueuelen 1 (Boucle locale) RX packets 20996 bytes 8495857 (8.1 MiB) RX errors 0 dropped 0 overruns 0 frame 0 TX packets 20996 bytes 8495857 (8.1 MiB) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0 wlan0: flags=4099 mtu 1500 ether b8:27:eb:6d:3b:7c txqueuelen 1000 (Ethernet) RX packets 0 bytes 0 (0.0 B) RX errors 0 dropped 0 overruns 0 frame 0 TX packets 0 bytes 0 (0.0 B) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0