I really hope you can get this issue resolved,for the sake of the kids and the PTO.
Your situation is exactly the reason we donated $$ to the school for new playground equipment instead of contracting with the company ourselves. The school district has legal counsel, facilities and grounds experts, and way more clout than our PTO.
Did you have a written contract with this company? What does it say in regards to the preparation of the area and the mulch requirements?
Also, have you talked with the powers that be in your school district? This may be an issue that they would want to pursue themselves, especially since the company is not responding to your requests.
It looks like we may need legal advice in dealing with a playground equipment company. We had a playground installed last fall. Unknown to us at the time, the playground area was not treated with weed killer or cleared of grass, resulting in the entire area being engulfed in weeds over the summer. Upon closer inspection we have found that the rubber mulch they installed beneath our playset does not conform to safety regulations. (The mulch is only 1-2 inches deep in many places and only 4 inches maximum at any spot measured.)
Does anyone have advice in dealing with a problem like this? The owners of the company have not responded to my requests for action. Will it require some legal action?