I bought a "B" class fare GIG-ATL-LAX-MSP-STL. When I had a flight change the Diamond Desk reissued as a "M" fare, dropping me from 150% MQM to 100% MQM in the process. Advised that I had a tiny credit coming I asked how, had she changed the fare class? She assured me the fare class remained the same. I only understood about the downgrade after the flights were completed. I protested and sent a formal request to Delta which was promptly and instantly denied. I was told that if they honored my request, no matter how much they might want to, it would create a precedent to do the same for others. Now what should I do? I am quite irritated by that, more so because my Delta Reserve American Express $30k and $60K 15k MQM each posted as ordinary miles and they seemingly don't want to correct that one either. I'm suspecting DL may want to drive me away. They may succeed.