The bailiff wrote on a receipt or document you paid voluntarily.

When a bailiff takes a money transfer from you for someone else’s debt, they write the words paid voluntarily. It is an effort to estop you^[1][2] reclaiming the money later,^[3] by pretending that you willingly gave the money to the bailiff on the debtors behalf.

If you can show the bailiff took the money transfer under the pain of enforcement, then that buries the bailiff’s defence because he dishonestly made a false representation to cause you a loss or expose you to a risk of loss.^[4]

Bailiffs must not take control of goods that do not belong to the debtor,^[5] or make threats of doing so to achieve a benefit himself, or another or with intent to cause you a loss.^[6]

^{[1] Estoppel, see: The Law relating to Estoppel Representation, 4th edition, 2004 at para I.2.2, Spencer Bower (out of print, try [2] below)
[2] See: The Law of Waiver, Variation and Estoppel, 3rd ed, Oxford: 2012. See paragraph 9.02
[3] Civil Procedure Rule 3.4
[4] Section 2 of the Fraud Act 2006
[5] Paragraph 10 of Schedule 12 of the tribunals Courts and Enforcement Act 2007
[6] Section 21 of the Theft Act 1968}