Where can I lodge complaints and who monitors compliance with licences ?

Since the liberalisation of the telecommunications market in 1998 and the corresponding changes to the law on telecommunications, relations between telecommunication services providers and their customers have been based on civil law. The basis of this legal relationship is the contract concluded between them. Any resulting disputes, such as disputed telephone bills, must therefore in principle be settled between the contracting partners or, if necessary, before a civil court. Since May 2005, the telecommunications industry has set up an arbitration service (ombudscom) for complaints related to telecommunications services.

OFCOM is the supervisory authority under telecommunications law over providers of telecommunication services which are offered in Switzerland.
On the basis of the law it ensures that licensees and registered telecommunication services providers comply with national and international telecommunications law, statutory provisions and - in the case of licensees - their licences (cf. art. 52, 53, 58 and 60 of the Law on Telecommunications (available in français, deutsch, italiano). If the Federal Office finds that a violation of the applicable law has taken place, it can apply to ComCom for measures to be taken or - where OFCOM is the licensing authority - take measures itself.
The measures extend from remedying the fault, confiscation of unlawfully acquired revenue and amendment of the licence through to withdrawal of the licence (art. 58 para. 2 LTC). In the case of infringement of the licence or statutory provisions which generate a profit, an administrative fine of up to three times this profit may be imposed against the guilty telecommunication services provider. If no profit can be ascertained or estimated, the fine can be up to 10% of the previous year's turnover in Switzerland of the telecommunication services provider concerned (art. 60 LTC).
In the case of violations and contraventions as defined in art. 52 and 53 LTC, OFCOM may impose fines of up to CHF 100,000.

https://www.comcom.admin.ch/content/comcom/en/Homepage/the-commission/organisation/frequently-asked-questions/where-can-i-lodge-complaints.html