I was on CUN-MEX-IAD flights departing at 6am and arriving IAD at 3pmish.
The first flight was canceled and I was put on a 10pm CUN-MEX the previous day. Obviously I am not able to change the flight online because I am on economy light fare or whatever(Even though the email conveniently has a button saying pick a new flights online).
I call them and they give me like 2 options only that are as inconvenient - departing at 8am arriving at 7pm, or departing at 10am arriving at 10pm. All on DL(ATL or JFK)
Aeromexico.com sees a ton of flights that will be perfect for me which they cant confirm me on. When I mention specific flights that work for me again on DL they tell me they can't confirm them for me, even though you see them on AM(like 30 options available they only give me 2). When I check EF I see buckets available on other flights as well(i.e. econ light, more convenient DL or codeshare), so I have no idea what bucket they are looking for(I asked the lady and she has no idea what I am asking for).

When I bring cancellation they tell me its not allowed because of the underlying fare. I asked to speak to a sup, not available so asked to call back.

Anyone know their irrops policy? Seems very backwards, have no idea why they cant confirm me on better flights...

Edit: HUCA did the trick. The 7th agent was able to get me on the flight I wanted.