How can I cancel a recurring payment to Dropbox?

I downgraded my Dropbox account a month or so ago from Plus to Basic as I retired from work and no longer needed it. However, the monthly payment is still being taken from my account by Dropbox. As it was made with a card my bank can't cancel it as it has to be done by Dropbox. I've followed all the help options thrown at me and there is no apparent solution other than what I've actually done. I chatted with someone from sales who was next to useless and apart from that there's a botchat but of course that only sends you round in circles. Anybody know how to contact a human being at Dropbox or has had experience of this issue and how to resolve it. Typical tech companies who don't know how to provide simple customer support. It should be a 2 minute job but I've already pulled my hair our for over an hour!