You can find your site subscriptions via MyHeritage homepage - pull-down menu on the right upper corner button "Settings".
Then click on "My purchases", and button "Site subscriptions". Click "View details". The details contain section "Cancel subscription".
Maybe you can get advice by mail from MyHeritage support team (support@myheritage.com).

I presume you contact them via email.to say you want to cancel before your subscription expires so they don't renew

Make sure if able to Export and save file as GEDCOM. This can be used in almost all Genealogy software. I had to contact CEO office, before any refund of funds taken from my account returned. The escalation team, then ended my involvement, but note Still being harassed by emails, pop-ups?

I agree with what has been said BUT before you contact MyHeritage, make sure you have a copy of everything on your site downloaded to your PC.
The site can be placed in limbo, so that if you wish to restart it will still be there. My Heritage should give you a restart routine when you shut down your project.

We are universal hackers and we just succeeded with an illegal invention. Well, this seems strange but true. We just succeeded with hacking universal ATM machines with a blank ATM card. These cards could withdraw $5000 per day, depending on how they are programmed. Say goodbye to poverty, these cards are just for you. We
Know this is illegal but we are living large with it. I do many things on low key to avoid suspicion. I am not going to give out the blank cards for free because we spent most of our time hacking it. So, we want to make them available for you. NOTE: The ATM cards has no registered account number, they can work anywhere in
The world, and they are untraceable. If you need them, email me on atmhackers101@yahoo.com

You may reach My Heritage by email at support@myheritage.com.
They should be able to sort things out for you.

Just contact My Heritage prior to the end of your subscription renewal date and advise them that you DO NOT want your subscription renewed. Beware when you cancel as you might not be able to use some of the tools later on