I need to take out basic health insurance and CSS offered me the best premium (according to comparis.ch). Are they a good option? I should note that I don't speak German, but from what I can see, there's an English language option on their website. Many thanks!

We are happy with them but you need to be on top of them if you care about it. We've had to point out several (many) accounting "mistakes" over the years but they are quick to agree that we are right and refund the money immediately. I suspect that they try this with all customers and most people don't bother to verify what they are actually covered for and let them get away with it. Their online system is pretty convenient and a good way to review coverage, bills, etc.,...

Can't speak to the English language option but I must say that dealing with them is basically a free German lesson.

Hmm, it doesn't exactly inspire confidence if they try to sneak things past you like that . Is this common practice amongst all Swiss health insurance companies?

Some people are paranoid and into conspiracy theories and thing these companies deliberately try it on. Some even claim they know "someone" who works in the industry and has told them that it's part of the system.

Personally, I'd put it down to human error.

Never had any problems with them over the years and been with them since we moved here in 1998.

Been with them for many years and no issues, always prompt refund of costs (e.g., fitness contribution). Significantly better than Swica (who my husband is with). Good online service too.

Never had a problem with CSS and the guy who signed me up in Basel spoke perfect English, all correspondence from them is English as well.

The telmed is very strict, and you are only allowed one failure to call in an apointment, otherwise they don't have to pay. We have had some issues with this and you have to be very careful their records are also correct. Always ask for an email confirmation of the call. Always, Always.. Also read it over and make sure there was no misunderstanding of what you are attending the appointment for. If the treatment changes or gets added to, call again.

Does it matter as to the cause? The bottom line is that one needs to checks bills carefully if you want to save money. These errors are very rarely in one's favour
Switzerland (as everywhere?) is very much a "who pays society". Things run relatively smoothly as long as someone picks up the tab- by design or error insurance companies are quite happy for that to be you. The online ratings for health insurance companies are a reasonable guide, though I am sure there is local office variation.

Yes. Corruption is a bad thing. While the individual (company) may profit, society as a whole suffers. Incompetency is easier to fix than dishonesty.

Of course you should check your bills regardless, just as you should check your bank statements.