You can disable (and re-enable) the 'Contactless' feature of your Transcash cards. To do so, log in to your personal area, My cards > Manage my cards section, then click on the button:
Security settings (for the black card)
Parental control (for a red card)
You can also request this by contacting customer service, by calling +33 (0)1 53 88 22 76 (Free Call) or from your personal area, 'Contact us' section.