All subscriptions are non-refundable, unless required by law. That includes subscriptions linked to X accounts that have been suspended, or that you have lost access to for any other reason. This also includes situations where certain subscription features are temporarily or permanently unavailable.
However, only in the case you upgrade to a higher priced tier on iOS, you will receive a partial, prorated refund for the remainder of your previous subscription if you switch tiers from the platform where you were previously subscribed, i.e., iOS. If you upgrade to a higher priced tier on web, credit for the remainder of your previous subscription will go towards your account and automatically be applied to future payments if you switch tiers from the platform where you were previously subscribed, i.e., web.