Broken Black&Decker Vacuum! Service Blames User for Faulty Product!

I purchased a Black&Decker cordless vacuum from Idefix. We only used it in December, and it stopped working. We took it back to Idefix for a refund, but they declined because the machine had been opened and advised us to go to the service center. After a week, we got a reply from the service center, explaining that the mainboard was damaged because of a blocked filter. We're confused. How could a machine that was only used once end up with a clogged filter and a burned mainboard? Moreover, they mentioned that if it occurs once more, it will not be covered under warranty. This brand is completely new to me. Just wanted to mention that the vacuum costs ₺6500.