First, please note that this is the public forum, not the support channel for billing, accounts,... so forum moderators and other members can only give guidance only and cannot personally perform the refund.
Because you purchased BlackCell twice and the earlier order is marked as refunded, compare the two BlackCell entries in your Xbox order history with your bank statement. Make sure the £25 charge you are seeing belongs to the refunded order rather than the newer purchase.
If the original order shows Refunded, ask your bank or card provider whether they can trace an incoming refund for that transaction. Microsoft confirms that an issued refund may take additional time to appear, depending on the payment provider.
If the bank cannot find it, contact Xbox Support and provide the two order numbers, purchase dates, and refund confirmation. Only the billing team can check whether the refund was actually sent or correct an inaccurate order status.
Thank you for your understanding