Being threatened with legal action on a cancelled policy

I cancelled my cellphone insurance with Pineapple on 26 August 2021, effective from the end of the month, as per Pineapple's terms and conditions.

Their app states the following: "You may cancel the policy at any time, via the App, and the cancellation will take effect at the end of your current policy month (i.e the day before your next debit order)"

A debit order went off my bank account on 1 September 2021, which I though they will reverse. As they did not reverse the debit order, I reversed it on my banking app.

I have received the following sms from OM Iwyze, who I suppose are the underwriters for Pineapple: "[1]Our records reflect that you reversed your premium yet you continued to benefit from the cover, please contact us on: *** urgently, to prevent [2]legal action. FSP&Ins. T&Cs."

I am now being threatened with legal action for a debit order I reversed that should not have gone off in the first place by a company I have no direct dealings with.

It seems that Pineapple did not inform their underwriter of the change in policy. Now I am the bad guy for taking back money that should not have been taken in the first place!

Please sort out your mess!