Hi,
generally Swisscom is not responsible indeed for this reason directly. If you have issues in the Devices itself, then it should be a problem for Swisscom to solve.
Please try to take Speedtests and take screenshots. Then try again also by Mobile Hotspot.
Then you should contact Swisscom again and also tell them from the Screenshots you have.
Alternatively contact the Apple or Samsung-Support for further Help with your devices - maybe they have broken parts or other issues.
Gruess, Cordial salids, Cordialement, Cordiali Saluti, Cheers!
Dominik