I changed my Apple ID and now i can't find my old contacts

Here's how you change the email address you use for your Apple ID:

1. Go to https://appleid.apple.com and sign in.

2. In the Sign-In and Security section, choose Apple ID.

3. Enter the email address that you want to use as your Apple ID.

4. Choose Change Apple ID.

5. If you changed your Apple ID to a third-party email address, check your email for a verification code, then enter the code. Learn what to do if you didn't get the email. --> If you didn't receive your verification or reset email - Apple Support

6. If you use services like iCloud or Messages to share with friends and colleagues, sign in to those services with your updated Apple ID. --> What to do after you change your Apple ID or password - Apple Support

For more details, read the document: "Change your Apple ID" --> Change your Apple ID - Apple Support

Unfortunately it sounds like you did not change your ID that way but instead created a completely different account. While you can transfer contacts it is complicated to both describe and do. You would also lose access to other things associated with the old account that Apple will not let you transfer, only hsare by setting up Family Sharing with yourself. You would be better off just going back to using the old account. However, now that you have created an account using the email address to which you intended to change the old one, you will need a new email address as it is quite possible APple won't let you use that one now for the new address for the old account.