Plazacorp Urban Residential Communities will not acknowledge their signed agreements... Internet

I purchased a residence from a financial institution that had foreclosed on the partially completed development.  Shortly after the purchase, the ownership was transferred over to Plazacorp Urban Residential Communities and I was contacted to select finishes.  This is where things turned strange:

- The finishes presented grossly contradicted the agreement of purchase and sale I had.  I had pointed this out during the 1 selection meeting I had and was able to resolve most of the discrepancies... that is the ones I was able to identify.
- Upon completion of the selection, it was I, the home buyer, that suggested the creation of a Document of Understanding to formalize the selections made.  Plazacorp Urban Residential Communities agreed and signed this document.  I also signed the document.
- During the PDI process I noted a deficiency with regards to a staircase installed.  The signed agreement between myself and Plazacorp Urban Residential Communities states that the staircase should be constructed of oak.  Currently the staircase is Pine plywood (not even solid pine).  Plazacorp Urban Residential Communities considers this a valid substitution as they feel it is of equal or higher quality.

Pine plywood is the same quality as oak?  I beg to differ.  A signed agreement is an obligation.  Stand up an honor your obligations, Plazacorp Urban Residential Communities.