Yes, it's not the most intuitive service to cancel.
But still, it's as easy as filling out a damned form.
Had subscriptions to the BE Archive and BE Story club. Fill the form out
with accurate information and you'll be all set.
Note on the reason you give: Don't be stupid and go off on a tangent. "No longer desire subscription" or "cutting costs." If you say "was difficult to use sign in," they could try to solve your problem to deflect a cancellation.