This is a common glitch with Instagram. I have been facing the issue while registering a new account on Instagram. I was astonished to learn that there are several other users who are facing the same issue. Unfortunately, there is no option to solve the error. However, you can try the method here:(https://fixyourandroid.com/fix/i-cant-sign-up-for-an-instagram-account/) . Good luck!!. Surprisingly writing the Instagram help will give you can robotic reply. It's better to use a new email address and try reporting or claiming the old account, if you are lucky enough you can get access to the account..