Contact E-mail change to previous (Main) Email

[#1]

I changed my contact email a few months ago and used another new email. But now I want to use my primary email again as the contact email, The email with which the account was opened.
But when I try to change it gives me an error "This email is already in use."
How can I use my previous email again?
Note: I did not open any other account with that email, nor did I ever try to open a new one.

[#2]

Hi MD Ariful,

We’ll have one of our agents reach out to you via a support ticket to assist you with changing your email address.

Thank you!