Bad costumer service

As a first time buyer I was very disappointed in the service for I went to the store and I bought some PVC ceiling boards only to find out that my contractor had calculated the M2 range wrongly and now I have more than 6 boxes of PVC ceiling boards remaining in my house and as I have ask them they told me that they cannot accept them back due to the fact that I had bought the material only in January 2021 of which I find it very strange because in other retail stores they would allow me to return them and opt to give me a voucher as opposed to cash which I am willing to accept as a as a new customer I would like the management of the store to give me a call and explain why can't they give me a voucher and allow me to return the goods for they are still in a good condition and I still have the proof of purchase.