Greetings,
A number of Swiss banks expect you to provide a confirmation of residence document from your municipal office when you close your 3a retirement accounts. At some banks this is the regular procedure while some banks only request this confirmation if they have doubts about your place of residence.
However, there are also banks which do not require this document at all, including UBS, Credit Suisse and some others.
If you feel that avoiding this extra cost is worth the effort, you can transfer your assets to a bank which does not require this document - then close your account shortly after. Just make sure that your current bank does not charge a premature closure fee or a transfer fee when you transfer your assets to another bank. Also pay attention to possible account termination fees and notice periods at your new bank. In most cases, simply providing the proof of residence document will likely be the more efficient option.
Best regards from Moneyguru
More on this topic:
3a retirement account comparison
3a accounts: Fees and charges to watch out for
Notice periods for 3a savings accounts