This could potentially be a big mess, particularly since you have not told us to which country your parents' account is set and where they are now.
There are multiple reasons for seeing that message. Try contacting Apple in the country to which the account is set. The person doing this will have to be in that country since Apple does not provide support outside of country. Ask Apple why it is locked and what may need to be done to unlock it. Sometimes it just needs for the account owner to contact them.
If Apple will not unlock it then the account was detected as violating one of Apple's terms and conditions (possibly by using an account extensively in a country to which is was not set). According to various posts, Apple may permanently lock accounts for other reasons (very broadly outlined in section VII-B of Legal - iCloud - Apple). If it isn’t apparent, contact Apple and ask if that is the situation, but don’t expect them to tell you why. You, or somebody who has managed to get access to your account, are likely doing something Apple is interpreting as account misuse (maybe it being extensively used in a country which is not the one to which the account is set?). You will have to see if your activities could be construed—rightly or wrongly—as meeting any of Apple's conditions in the legal article. You will need to create a new account and stop doing things the way you have been that may have caused the other account to be locked.
In this situation you may be able to still use your equipment with a new account or even no account at all. Apple can completely reset a device if a person can provide sufficient evidence of valid ownership. Check the requirements and steps at: Activation Lock support request - https://al-support.apple.com/#/additional-support Apple says, "Proof of ownership documentation is required," but does not detail what currently constitutes proof other than it “must include the product serial number, IMEI or MEID.” Apple may typically require the original receipt* issued by Apple or an Apple Authorized Reseller. If Apple resets the device this will give you access to the device but won't restore access to the account used to lock it. There is nothing that can be done to expedite an Activation Lock request.
*Apple recommends you "Keep your receipt after you buy an Apple device" --> Keep your receipt after you buy an Apple device - Apple Support
