Do you still want data, do you use the watch independently of your phone if not, cancel the data plan and carry on using it? If you still want data you could switch to a sim only plan for the watch.
if you do decide to stop using data you will need to remove the data plan from your watch (and cancel with EE) and then unpair and repair your watch or you will be plagued with messages about it not being able to active the data plan you have removed.
