I have deleted my account, but my device is always on this one so I can’t add this device on my new account. Have you got any issue ?
This is expected behaviour - see the reference section of the docs for more info.
There is the option to pay TTN support and create a ticket asking very nicely for them to adjust this for you. I was able to open a case this way and get it fixed. It may be cheaper to just order another device, depending on what your end device is.