How to calculate cut-off frequency for T section high pass filter?
With no load , the right hand 2C might as well be a short circuit and the 3 reactive parts only behave as a 2nd order high pass filter with high Q at the breakpoint. 

With a resistive load the CR LPF adds a 3rd order HPF result.

( In theory with 0 ohm source and infinite load , the breakpoint has infinite Q , but in practice limited to Q = few hundred from ratings of components e.g. 100 is not hard, 1000 is not likely)  With a load R this reduces by Z(f)/R at resonance.