Virgin Active - Membership cancellation

After my membership expired in May/June, I contacted Virgin Active to find out when and how I must give notice.
As they told me, I gave notice via email on the 23rd of June 2021.
At the time their systems were off but they acknowledged receipt of my cancellation and that it will be processed.
They kept debiting my account thus I stopped the debit order.
Now, 6 months later, they consistently call me saying my account is in arrears and was never cancelled.

Useless contact agents!