Dear "Verified Private User".
Could you please send us an email or contact us in any other way so that we can take actions regarding this matter.
We would love to dig deeper to see why "20 boxes were not used", was there a change in the layout on the day of installation? Was there any last minute troubleshooting due to unforseen construction site situation? As you know, we are adamant about the client being on site with our installation team on the full day of the installation to go over everything together, so the communication is transparent. You, as our client would be part of the installation process and would know exactly why changes are needed. Perhaps the order was incorrect or delivered wrong?
Was there custom work that you as requested and wasn't indicated pn the layout?
We are listing these circumstances because they are not uncommon in a complex project such as a kitchen design and install.
"Estimates" are exactly that, estimated costs based on the piece of paper with 2D information. However, on-site and in person, if the plan doesn't work (as one of the instances why the price can fluctuate), you along with the installers will troubleshoot to find the solution. Sometimes this involves tweeking the design, and as such results in change of order and material.
All this is hypothetical and we can list more reasons, but we would prefer to talk to you directly and with facts, so please reach out to us.