To keep your Apple ID account secure, see the following Apple articles:
If you think your Apple ID has been compromised
If you think your Apple ID has been compromised - Apple Support
See who has access to your device or accounts
See who has access to your iPhone or iPad – Apple Support (UK)
Delete suspicious content from your devices
Delete suspicious content from your devices – Apple Support (UK)
Check your Apple ID device list to see where you're signed in
Check your Apple ID device list to find where you're signed in - Apple Support
- if you see devices that don't belong to you, delete from your account.
Personal Safety User Guide -> Personal Safety User Guide – Apple Support (UK)
Manage and use your Apple ID -> Manage and use your Apple ID – Apple Support (UK)
(if you haven't already done this) Two-factor authentication for Apple ID -> Two-factor authentication for Apple ID - Apple Support
Change your Apple ID password -> Change your Apple ID password - Apple Support
- Create a strong password for your Apple ID, It is best if your password consists of eight or more characters and include upper and lowercase letters, and at least one number. You can also add extra characters and punctuation marks to make your password even stronger.
- Never provide your password, passcode, security questions, verification codes, recovery key or any other account security details to anyone else. Apple will never ask you for this information.
Then see this Apple article: What to do after you change your Apple ID or password
What to do after you change your Apple ID or password - Apple Support
See -> Contact Apple for help with Apple ID account security
Contact Apple for help with Apple ID account security - Apple Support
Never jailbroken your iPhone.
