1. Cobbcustomz, wiring subs in reverse polarity in and of itself shouldn't have noticeable effect on their outputs, UNLESS the subs are wired out of phase with each other, which, like KuttinEdge mentioned, leads to cancellation.
2. B16a2VTIguy, here's no "wrong type of amp" for his subs so long as he's powering them correctly. The belief that you "should" have a monoblock is BS.
3. Yankee81116, if that amp is 600W RMS at the right impedence, I see no reason why it's necessary to upgrade it or why it's an impairment to the output. You should give the model number of the amp, so that we can make a better judgement on whether the subs are being powered correctly.
4. Exempt, that sub is not 1200W RMS max - it's 1200W max power. The RMS power handling on that model is 300W. Destroying a speaker from underpowering it is usually a result of overpowering it, not distortion... when you set the gain up too high to compensate for a low output amp, you clip the signal and cause the amp to double its output. The sub is most likely damaged from the insufficient thermal or mechanical handling capability, assuming that the sub cannot handle the doubled output to begin with.
5. Yankee81116, I would not try to bridge that amp if I were you. Your amp in all likelihood is bridged to a stable 4 ohm load. Your subs are SVC 4 ohms. Running them in parallel off a single channel would give you an effective 2 ohm load and could set your amp into protection mode or cause it to overheat.
** Are the subs in a single chamber enclosure without an internal divider? If you're still getting bass (albeit less bass) from your setup and it's in a single chamber, it's possible that you just blew one of your subs. If it's still wired in stereo, use your head unit and change the alignment to full left and full right and see if it plays in both settings. If it does not play in either left or right, then you know that side's the source of the problem. Or you could just have one sub hooked up at a time when testing to make sure they're individually still good.