Refunds can be issued for a service that is not working, provided the problem occurred on the provider's end. For example, a refund may be given for a particular number that was not able to receive and make calls for a non-working period. Sometimes a replacement of the number may be offered instead. But if the number itself was working, i.e. was able to make or receive incoming calls, but the problem occurred on the user's side (e.g. due to settings on a SIP app, traffic blocking by the internet provider, etc.) no refunds are made.
You can apply for a refund for a particular service from your personal account in the menu "Support" --> "Submit a request".