There is always more than one way to skin a cat.
Go to your bank / credit card provider / whoever you pay through, and cancel the payment authority.
At renewal time, they will try to claim payment, and it will be refused.
They will send you a huffy e-mail saying that as your payment has failed they will cancel your membership.
Job done.
HOWEVER - I am still happy with FindMyPast, despite their move to the abominable "fuzzy logic" which ruins my carefully thought-out searching strategies. Your results that may be there not showing up on searhces may be due to an anomaly which I have identified. The data set which they call "England Births & Baptisms 1538 - 1975", and its counterparts for marriages and burials, does NOT appear to have had the location metadata properly entered. This has the result that if you specify a location in the relevant search field, ALL results from this data set are screened out. Once you are back into the seventeenth century, this is often the ONLY data set with the entry you are looking for. Result ... you have to do a search of the entire country and then sift the hits manually. It can be tedious ... but still not as tedious as wading through loads of microfiches of parish registers when you do not know which is the relevant parish ...