At a minimum, you need to get your home phone number changed to one that is unlisted so that OW cannot contact him. He also must change his cell phone number. If he protests that he cannot becuase he uses his cell phone for business, then you can get him another one and keep his, giving him any business messages until he can tell enough contacts his new phone number. You need to get the mail at your house, and he needs to give you the passwords to any and all email accounts he has. It will be hard enough for him to avoid calling her as it is, but if he won't agree to shut off her ability to contact him, then he's very prone to a relapse -- it happened to my W because she thought she could still talk to OM as "friends".
The LORD is near to all who call on him, to all who call on him in truth." (Psalm 145:18)