Top carpet underlay deteriorating in four years time

In March 2019, I used this company to put a carpet in our home @R12 500 (Quote QU125378). Four years later, our tenant starts complaining about the orange underlay that is deteriorating and falling through the cracks of the wooden floor. We get the same people in. To replace the underlay and put the existing carpet back, they quote us R8000. R13 500 to redo the entire story. On their website, they give you the option to inquire about the warranty of the products you purchase from them. I have requested information on this, but I am not too hopeful. After initially replying to my email where I questioned them about telling the tenant that the carpets are very old, they are now ignoring me. After investigating this on the internet, it seems like the underlay should at least last as long as the carpet. Was there something wrong with the underlay? Should the same company charge me this much for something they themselves installed four years ago?