The MAX232 psu generates +/-7v with a 7k load, only +5/-4 v with a !k load. It requires a +5v supply.
If you just want to to the job with a high voltage supply a boost convertor would be OK - but you then also need a suitable circuit to drive the piezo.
The op has already achieved 17vac from a 3v5 signal using a series resonant circuit. Since the waveform will be sine-ish that implies 48v p-p.
Allan