Anonymous participant you made it sound like you were trying to have two visas at the same time - just say you applied for a DTV and are going to cancel your Non - O at the embassy or immigration? I believe you needed to go to immigration and cancel first and they would have provided you 7 days to obtain a new visa status
I don’t believe you can have multiple valid visas at the same time, if issued it will be likely caught by immigration on arrival etc with their system or passport stamp review - one of the visas needs to be cancelled prior to, you should also have disclosed having a active visa already