Email OTP Authentication

Our use case is that our user can only register with password-less flow to register by sms and our user can input their Email and valid it throw Email Otp, it depends on the user.
At first we want to do it by validating user’s email by password-less flow to create an email account and link it to the users sms account. But there is problem that it may link two consumer account into one due linking to same email, and one consumer can link multiple email which do not suit our use case. Is there any recommendation way to achieve our requirements? Thanks very much.