I've been trying to create an Upwork account but it doesnt accept my phone number. I tried to create an account in the past with that number but that account has been alread deactivated.
Thank you in advance for your help.
Upwork does not allow you to create multiple accounts. It is a violation of Upwork ToS. This is something that Upwork looks for and actively takes measures against users who violate the rule.
You may not create a new account, whether with this already-used phone number or any other phone number.
What you will need to do is reactivate and use the account you created earlier.
It sounds like you will need help from Customer Support.
You could create a Help Desk ticket, but you might just wait to see if a Forum Moderator intercedes on your behalf, and puts your situation in front of the right people. I recommend waiting a few hours to see if that happens.