This is not a question of customer service, but of following the rule of law and of risk allocation.
Many carriers are offering vouchers in place of refunds, but at a substantial premium, e.g. 20% or more. If a passenger wants that and is willing to give up his use of the cash in return for the premium, that is a win-win. However, the bottom line is that by contract, EC 261/2004 and US DOT rules (if a flight to or from the US) a refund is due if the carrier cancels the flight.
Refunds should be processed within 7 business days and if one has not heard back in that time (or has been denied), moving to a chargeback on the 8th day is simply prudent.