Hi My son has my old phone and has removed all my contacts and is not copppying allhis new contacts into my phone but has put his apple id in. How do I get my contacts back and stop his saving into mine?

1. You should have wiped your iPhone clean and removed all your information from it, before handing it to him. Right now it's a mess that may be very hard to resolve.
2. The first thing to do, is to make sure your Apple ID is no longer sinned in to anything on the iPhone. You say he's signed in to his Apple ID, but have not mentioned where. There's 4 different services an Apple ID can be signed in to on an iPhone. Media & Purchases, iCloud, Messages and FaceTime. Where exactly did he sign in?
3. You may be able to restore your contacts if you store them in iCloud from the archive there. Log in to https://icloud.com and scroll to the bottom, then click on Data Recovery and then on Restore Contacts.
4. click here ➜ If you accidentally deleted your calendars, bookmarks, or contacts from iCloud - Apple Support

If you use a different email account to store your contacts, then you will need to go to its website and see if there is a way to recover them from there.

Once you recover them, or once you are sure they cannot be recovered, then wipe your iPhone completely so it is no longer tied to your new iPhone or other devices. Then let your son set it up as new. click here ➜ What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support