Assuming you're talking about Digicell, which does use SIM cards, and not Smart which doesn't, the answer is still probably that you've left it too long and you'll have to buy another SIM card (and of course get a new number).

After a maximum of three months they expire your credit and your phone will only work to receive calls. After a further indeterminate period (I haven't been able to get a clear answer from BTL) they cancel your SIM card altogether. From that point that card will never again work. I suspect you've reached that point, though you can check by putting your card into your functioning and charged phone and see if someone else can phone it. If they can't it's probably dead, though I would take the card to a Digicell office when you're next here and get them to confirm that.

You shouldn't have a problem buying a new SIM card, though they do run out from time to time. Try BTL first, then all the cellphone shops. Alternatively, see if you can buy one at the international airport on your way in - I have seen them for sale there.

I don't know whether they re-use the phone number from a deceased SIM card. If they don't I don't see any reason to kill it, but no doubt there's some commercial reason.

If you're happy to buy and use another phone then you might consider SMART anyway. Most people who have made the change say they prefer it.