What do Amazon mean by Brand owner?

I am just going round and round in circles here with Support.

So - I sell the same same slippers in 3 different sizes
They are all made by the same manufacturer (lets call the manufacturer XYZ). The GTIN’s when looked up on GS1 confirm this.
The slippers have the logo (so Brand) from a well known film and the manufacturer officially licences the Brand for the slippers (lets call the Brand ABC)

At the moment each size is in its own listing and I want to combine them into a variation listing so customer can see they come in multiple sizes and choose the size they require.

Unfortunately, whoever setup the original listings used ABC in the Brand field for 2 of the sizes, but XYZ as the Brand in the other size (probably the listings were created by different sellers).

As such - Amazon will not let me combine the 3 listings into a variation listing because Brand is different. I have opened and re-opened cases but just keep getting told the exact same stuff - Namely that they cannot combine them as Brand is different, and that Brand cannot be changed on the one size as only the Brand owner can do so. They tell me they have contacted the Brand owner to ask them to make the change.

Now - who are Amazon contacting?

It is very unlikely they are contacting Brand ABC (I do not believe ABC is listed in Brand Registry, but even so the one I want to change has XYZ down as Brand which I would like changed to ABC, so surely it would be XYZ they contacted)

They are not contacting the manufacturer XYZ to make the change as I have checked directly with them (even though the GTIN shows the product belongs to them).

So, assuming Amazon have contacted anyone, they can only have messaged the original listing creator - which is just plain stupid as they are not the Brand owner or the owner of the GTIN and they are not even selling the product anymore (I know this as a fact).

So - when Amazon say they have contacted Brand owner - who do they mean?

I have even tried suggesting to Amazon that instead of changing Brand of the one odd size to XYZ they instead change the Brand of the other 2 sizes to manufacturer ABC so that they all match - but again the answer is no.

I have even asked the manufacturer to try and make the change - but again they get told they are not the Brand owner so cannot do it.

It should not be this difficult. Anyone any ideas how to proceed further?