Hi mate,
Unfortunately the link to the ebay auction wasn;t working so I'll have to try and guess some things...
1st you need to check the RMS value of both the sub and the Amplifier. Thats the real power output not the over inflated peak power that they normally print on the packaging or casing. Its still measure in Watts tho.
You need to make sure that the max output of the amp doesn't exceed the recommended operating output of the sub, this could have made it blow by putting too much power thru the cone and working the magnet too hard.
Most amps have a "gain" control on them, this is basically a power switch, you should always install an amp with this turned right down and gradually increase it until you're happy with the sound.
The other reason the sub could have blown could be that the amp wasn't filtering out all the other levels of sound.
Low frequency bass notes are created by slower, longer movements of the cone.
If the amp was sending higher frequencies to the sub, it's possible that it could make it work overtime and fry it that way....
Its worth checking the operating limits of the amp, most have crossovers or filters built into them to send the right sound to the sub...
It could also be that the wiring of the sub inside whatever enclosure you have shorted out the sub? were the + and - touching? Especially if the sub made a weird sound when you turned it on?
Are you sure it was wired in correctly? Does the permanent live have a suitable fuse AS CLOSE to the car battery as possible? If the permanent live is going through the bulkhead, did you use a rubber grommet or something to make sure its not hitting bare wire?
Where did you take your remote/ignition live from?
Was the amp earthed as close as possible to a suitable point?
However, its most likely that the 7 hours of use just wore the magnet out
