Trying to cancel the IMDb pro account of my late father - but I don't have log-in details

Hi. For some reason, my mother's bank account is still being charged for my late father's IMDb pro account. I'm unable to access the account despite having his email and password. This is because I need OTP verification from his mobile phone...which is no longer in service as we cancelled his contract when he died. Can someone help? My mother is being charged £19 (or thereabouts) a month for a service she simply doesn't use! Thank you!