Update for educational purposes.
screen shot of final bill generated on the 12th (as seen above) No mention of refund. This screenshot was taken on the 22nd.
Next screenshot taken on the 23rd, Notice the refund section.
£23.05 taken out of account on the 13th June. No refund issued so far. I was not alerted to this alteration to my 12th of June final bill.
Except for this forum I have not yet contacted BT about this. BT does have an interesting way delivering its final bill.