Product tampering

I purchased a home theatre speaker package from this branch and upon putting it on found a fault with the subwoofer which I took in to the service department at the branch. The repairer reports that the unit was tampered with and as a result my warranty was voided and the speaker was not repaired. So the service manager informs me there's nothing they can do and I must come pick up my speaker which was not repaired, she says they will not replace the item. Totally unacceptable and poor customer service. I am still waiting for some feedback almost 4 weeks after sending in the sub to the service department.