I have very similiar ( if not the same issue) .
I have an HD Account ( Mycelium) with zero Balance, and a Single address with All my BTC.

I tried using my 12 word Master seed but it only brought up my HD Address with zero funds.

I have a separate Address for my Single address, and im not sure if the Private Key is the same for both.

Nervous of making a mistake by transferring funds to HD ACT Bc im almost positive the btc wasnt in their at time of fork.

And im pretty positive i wasnt given ANOTHER 12-WORD Master seed for my Single Address..

So IM LOST ON WHAT TO DO , ANY HELP PLEASE?