Let me see if I get the OP story right.
1. Bought an economy ticket LHR-HKG-DPS.
2. Paid 800 British pounds sterling
3. A day later wanted to upgrade to J or F.
4. Was told he/she couldn't up-sell.
5. Bought a new ticket for travel in first class.
6. Was told by agent he/she could have up-sell.
7. Lost the initial 800 payment.
8. Email customer service to complain.
9. Posted on CX fb page.
10. Need info on who to contact @CX to complain.
OP, what kind of ticket you had that you lost the 800?