Ledger Support can't/won't help me and insist that this address did not come from my wallet or 24 word seed.
How would they know? Does Ledger not allow the creation of Segwit compatible addresses (starting with a 3)?
I notice on the blockchain that there is an exact same address relating to BCH - not sure why this is?
That's normal: BCH uses the same addresses. The address isn't funded, so just ignore it.
Anyone got any idea how I can access/retrieve my coins?
Have you tried
IanColeman? If you try this, do it offline from a Live Linux DVD (running from RAM). Don't risk compromising your 24 words by touching an online device.