Attribute has already been claimed by another brand?

Hi,
Does anybody have any advice on how to update the title for an ASIN when Seller Support explain that attribute has already been claimed by another brand?
We own the rights to the brand for said ASIN, however this ASIN was listed on a different seller account prior. We have reached out to Seller Support and Brand Registry but keep hitting a brick wall.
Any advice, or workarounds would be really appreciated. We have tried deleting/re-listing, tried uploading feed files to overwrite the content but nothing works.
Thanks in advance