Hi Nancie,
There is a period of a few week where a new mattress will break in as the foam layers lose some of their initial “false loft” and the covers stretch a bit and become less stiff and there is also an an adjustment period for most people as they get used to a new sleeping surface. The mattress in the showroom was probably also broken in so it would be normal that it would be softer if the ILD’s were the same as what you received.
The break in period and adjustment period isn’t usually dramatic though with latex and based on your description it sounds like there may be more going on. There are also some other possibilities that can affect the feel of a mattress that are mentioned in post #2 here (including your mattress protector or a mattress pad or even sheets and bedding in some cases). I would also keep in mind that many customers notice a difference between a new mattress and what they tested in a showroom so the first assumption of most stores is that what they are “feeling” is just the normal breakin or adjustment period.
Other than ruling these out though as possible causes for any difference between what you tested and what you received … I would do the same thing as you are doing which is confirming both what was in the mattress that you tested and what was in the mattress you received.
If I understand you correctly … your mattress has a 6" support core of 44 ILD latex and then you have a softer comfort layer (inside the mattress so it’s not a topper?) that is probably a 28 ILD but the showroom model you tested may have been 19 ILD. Is this correct?
If you checked the “codes” (and I’m assuming you mean the tag that is on the layer when you unzip the cover shows 19 ILD) then it should be no problem having them replace it with the firmness level that you wanted and tested as being most suitable once you know what it is (regardless of the ILD).
Does your mattress also have the tag on the layer that shows what its firmness is as well?
In any case … once you can confirm (with their help) what the ILD was that you tested and what you received then I would think that they should be more than willing to switch your comfort layer with the one you actually tested because that’s an option that you mentioned they offer anyway even if the ILD’s were correct.
Once you confirm the ILD’s of the showroom mattress and the one you received I would hope that the problem will be taken care of.
Your experience is unfortunate but hopefully they will help you take care of this quickly and your next post will be about how this was all resolved 
Phoenix