Unable to add device [Conflict error]

I am using a inucleo lrwan, and sending data to TTN, from there to cayenne.
I had registered my end device at cayenne from my guides account, earlier the device was registered from there in his cayenne account, after testing it yesterday, today we were not able to find the device registered in his account.
We deleted his account , now I am trying to add device from my account but same ERROR Conflict is showing.
[ *cayenne name for end device same as webhook name-> earlier when i faced simmilar problem this resolved my issue]

please guide how to resolve this as this is part of my final year project and now i am unable to access dashboard.