First, the last agent you mentioned was not telling you the truth (or you misunderstood her). If the booking is cancelled it would not show on MMB.

I actually had a similar case before, except I corrected it immediately before the booking was gone. What happened was that the agent who took your CC info on June 17th forgot to remove the TKTL (Ticket Time Limit) in the PNR, resulting in auto-cancellation. The PNR is, however, still retrievable, and the history would show that you have given the CC info and which agent received (from) it.

What I would do is to demand MPO to reinstead the confirmed booking for you. CX has internal procedures regarding how to reinstead a booking cancelled by mistake, and you fall into that category. If they say no supervisor can answer your call, ask them to call back and ask them how long you need to wait for the call back. Ask the supervisor to look at PNR history and the phone call recording. Be firm (unless the F cabin is actually fully booked, in which case you might need to give them a bit flexibility).