I had a work thing in Los Angeles 2 weeks ago, I booked 3 rooms with Westin Bonaventure.

Room #1 for myself for 3 nights for 3 nights (6th-9th)
Room #2 for a colleague of mine for 2 nights (6th-8th), their names are entered in the system during checkin
Room #3 for another colleague of mine for 1 night (6th-7th), their names are entered in the system during checkin

Marriott only credited 1 elite nights (6th-7th) to my account, so I submitted a missing stay request, and they replied that everything is credited correctly.
I submitted another missing stay request and reminded them that I should be credited for 3 elite nights not 1 nights, then I received another reply that "everything is credited correctly, it's Marriott's policy that one can get credit for max 3 rooms and elite night for only one room".
So it looks like they conveniently chose that single night Room #3 to qualify for elite night.
Something similar happened last month when I stayed in the same hotel for 2 nights and then extended 2 more nights for a total of 4 nights, they only credited 2 elite nights, when I ask them on the phone, they added the 2 elite nights back without admitting there was an error, only keep saying everything is correct.

I'm really frustrated at this point and really considering switching to another loyalty program.
Am I asking for something that I don't deserve?

Is it the Hotel's, Marriott's or my own fault on these kind of issues?

Please Flyertalk community give me some feedback.