You can subscribe to Apple services like Apple Music as well as in-app services from various third-parties. You can see all of your reoccurring subscriptions in either iTunes on your Mac or in Settings on your iPhone or iPad. From there you can change the subscriptions to other plans offered, or cancel them. In many cases you can cancel a subscription but still use it until the next renewal date.
If something is wrong with your Mac, either you or the tech repairing your Mac will need to access the special diagnostics mode. You can do this by restarting your Mac and holding the D key. The results could give you some insight into the problem. See https://support.apple.com/en-us/HT202731 for details.