It is entirely reasonable for a carrier to apply its fare rules to voluntary cancellations. It is a customer service gesture to amend those in the customer's favor, e.g. customer may cancel an inflexible ticket for a credit.
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It is both unlawful and thus unreasonable for a carrier not to abide by the law. This includes applicable Regulations such as EC 261/2004 as well as contractual obligations.
For the broader audience, it is important to protect oneself through the chargeback process if a refund is requested under the contract, fare rules, or a specific enactment such as EC 261/2004. That ought to occur in the time-frame for the provision, e.g. on the 8th day under the Regulation. One may always withdraw the chargeback if the refund appears. Don't let a carrier string you along for 120 days and then start a chargeback process which may take that long as well. Moreover, there are many jurisdictions where there are time limits for chargebacks, although those may be extended when the service was simply not provided.
While we are generally used to handling chargeback requests on an informal basis, it is important to pursue them as required under local law. If a phone call suffices, then a call it is. But, the requirement generally requires a written request sent to a specific address. If that is the case, this is what one ought to do (even if there is online provision which one also utilizes).
Don't let this become a question of allocating fault. It is not. It is simply a means of allocating risk. Individual consumers are not in the business of lending cash to large entities.