My contacts keep getting deleted and new ones appear. Also it seems as if someone is sending messages from my phone away from my phone.

No one is sending messages or email from your iPhone away from your iPhone.

If with an email account and the account is an IMAP account, your account may be hacked. Change the password for the email account.

Are you syncing contacts direct with a supported address book app on your computer, or are you syncing contacts over the air with an email account that supports it? If the latter and the same email account that may be hacked, changing the password for the account will resolve both.

OK while I am told this can happen I have this happen about twice a week I have put in new contacts and by the end of the week they are gone. I also have contacts in my contact list that I have no idea who they are. I have changed password multiple times but it still happens and it has been happening for about a year. Any ideas

What are you syncing your contacts with, the computer, an email account, Exchange, iCloud? Or another cloud service, such as Yahoo, Gmail?

If you share your icloud account that could explain this. And if you don't share it then it may have been hacked. Change your password.