No devaluation surprises me, but I sort of doubt they would change fare classes or MQM earning so quickly after just having changed it several weeks ago. For one thing their IT couldn't handle it.

OP, IMO you got an ignorant agent. Happens all the time. Call back and talk to someone else. Or look up rwoman's thread about how she corrected mistaken reduced earnings on her LHR-USA flights, then use the same general procedure but adjust to your own case. With a little patience an legwork you should be able to fix this.