Shocking service for cancellation of membership

I really can't say anything good at the moment. My fiance wanted to cancel his membership at Stratum, seeing that his company now has their own gap cover. I filled in the form on the 31st of October (my effective cancellation date) and sent it off on the 1st of November. His debit order goes off on the 28th of every month. I didn't hear anything from them and assumed that it was fine (never assume). The debit order went off on the 28th of November. How is this possible? Now their querying the effective date on the form and saying they can't backdate. I want a refund for 28 November please. This was not my fault as I have the email where I sent this on the 1st of November.