Have had several missed calls from this number over last 4 days - don't leave a voicemail and can't call it back - just get dead air really strange who the heck is this?

That's exactly who it is. It's the Fit n Fast in Paddington, Brisbane.

I think this is a gym in Paddington Qld - Fit n Fast - I keep getting missed calls from them too! and they never leave a message.