Hi @Immico and welcome!
I’m confident it’s not a write off of your account. Account credits are not the same thing as refunds. Account credits remain on your account and are applied toward future monthly bills.
Should one choose to leave before the account credits are used up, they won’t necessarily be refunded. I’m not saying that’s how it should be but typically that’s the way it is.
I understand you have an issue with WiFi calling, however, this isn’t the topic in which to have that conversation.