Hey ganfoud, to be honest I wouldn't be surprised if they changed the rules recently. This change would be very much in line with other major hotel chains, tightening their rules and not extending elite benefits to third-party bookings... It's a shame that it also covers corporate travel agencies because in that case customers doesn't have a choice... Maybe it will make sense talking to your corporate travel agency and asking them to talk to their Melia contact? I don't thing that the corporate agent earns anything from this transaction, so you should be awarded those points.
Please report hen you anything back from CS.