It is best not to interfere with Tails' network settings for secuirty reasons, it is set by default to route all traffic through TOR.
What it looks like is that your ISP sees that you are using the TOR network and that's it. This is where everything ends for him.
The safest option, in my opinion, is to use a Mobile Router with forced LTE mode, on Linux, of course, such as OpenWrt, with a VPN client installed and a killswitch rule forced by the router.
Additionally, a SIM card for the pole, or if possible, buy an eSIM prepaid card (e.g. Nomad application) - OPPs have a huge problem with this.
A router that runs on OpenWRT - Mudi from GL-Inet.