The first step to canceling the HBO Max subscription is to find out who is billing you for this service. You may have either signed up for a third-party billing provider or through  https://www.maxcom-providers.com/

For instance, you may have used the HBO Max mobile app for this purpose. Find the right answer to this question with these steps:

Head to HBOMax.com.
Now, on your mobile device, click on your profile. Choose ‘Settings’ and go to ‘Subscription.’
On a PC, tap on your profile. Now, select ‘Settings’ and locate ‘Subscription.’
If you are using a smart TV, hit the ‘Settings’ icon followed by your ‘Account.’
These steps will let you find out through whom your subscription is billed.