Bringing up my experience in RESOLVING this issue. Exact same as your own and passing it on for the next guy.[br]
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I ended up taking a craft knife and using the tip at a very low angle to stab the black plastic on either side of the centre line.
I came in from the top of the phone, ie Camera side and used the knife like a chisel, the black plastic popped out in two halves. Avoid hitting any copper contacts.
Due to the amount of force used around small components I do not recommend this unless you are willing to damage the phone if it goes wrong, however, I got a working phone after this and no more battery issues on replacement. Go figure. Last chance saloon option here.