I felt being cheated. I paid RM4100 for my house grille (small double storey) and was told it's coated solid bar 1cmx1cm. However, after 5months, I see the rust start appearing. And when I knock knock on the bar, I feel like empty bar. How to verify whether it's really a solid bar?

When I knock on the bar, kong kong kong, I realized it is hollow, though not 100% confirmed. I ever visited another grille supplier and feel the solid bar sample. Thus,, I conclude mine is not solid! I'm planning to confront the supplier. How should I tell them? Sigh...