My switch to a standard Quickline SIM worked perfectly despite the language barrier.
I discovered that my free data sim from my old provider (Sunrise) is valid for life so I can keep that for internet at home even though I ordered a chf5/month SIM card from Quickline for this purpose. Currently using a small Huawei dongle but on advise from @sedot (Feedback on using 4G / 5G routers instead of copper wire - #27 by sedot) I will buy a better quality router (Huawei B818 CPE / B818-263).
Thank you Moustachians for the Quickline tip. 