Short answer. If you deleted an Instagram account by mistake, open the email Instagram sent and use the link to cancel the deletion while that mail is live. A disabled account is not deleted. If the login shows a disable notice, appeal that notice instead.
An Instagram account deleted by mistake is a deletion you, or someone with the password, started. Instagram’s help page says a deleted account cannot be restored once that process finishes, and that the cancel path is the message they send you. A disable notice is a different problem with a different button.
Use the deletion email first
Search the inbox on the account, including spam, for Instagram mail about deleting the profile. Open the message and use the cancel link in it. Do that as soon as you see the mail. Screenshot the email before you tap, so you have proof of the date.
The profile is simply gone and the email confirms deletion is finished. Instagram’s help page says that account cannot be restored. You can open a new account on the same email later. The old username can stay taken.
Send the username and the email screenshot if you want us to read which of those you have. We file disable appeals through Meta’s own official channels. It takes a few days. Start a case on the contact page. How it works is the three steps. We never ask for your password.
Instagram emails a link to cancel a deletion you started. Use that link from the inbox while it is still in the mail. After that, Instagram's help page says a deleted account cannot be restored.
I do not see a cancel email.
Search spam for mail from Instagram about deletion. If there is no mail and the login says disabled, you are looking at a ban, not a deletion.
Someone else deleted it with my password.
Check for a deletion email and a security email. Save both. If the screen is a disable notice, appeal it and say the account was compromised.
Do you need my password to restore it?
No. We never ask for the password. Send the username and any email from Instagram.