What does it show for resistance on your topper? Is it a steady reading, or does it change?
Sounds like you may have squashed the center pin down a bit, and are getting a bad connection. (IIRC, the 30 has a floating center pin to prevent that from happening...)
If that's the case, the quick fix is to wiggle the post up a hair. Turn it off. Then using a small screwdriver rock around the circumference of the pin, gently. 1 mm lift is probably all you need.
And yes, after a couple months, I'm not surprised they won't take it back. I'm a little surprised, though, they didn't try the pin lift to help you out.