If your account hasn't been active for longer than two years, chances of reviving that character are slim. You can try the "Return to Vana'diel" feature, but back then unactive accounts were kept on the server for three months then they were deleted. Only last year, SE removed that, so unactive accounts could be reactivated at any time.
You can't unlink your POL Account from the Gamertag it was registered with from what I was told by SE support last year (as I wanted to do the same), as any achievements you've earned and locked to the aforementioned account. Also, payment option wise, you'll need to create a Square Enix account and set payment up through Square's online site, instead of via PlayOnline as SE closed all services that offered about 16 months ago when they set up their new system. You can still pay via a Credit/Debit card, but also by a third party online service called "ClickandBuy" (which was rated by the US "Better Business Bureau" with a 'F' rating...).
My cousin lost his POL account information and tried to get them back by contacting SE Support, but was told that unless he had the registration codes (in the back of the manual) for the content allocating to the account - FFXI, Rise of the Zilart, Chains of Promathia, Treasures of Aht Urghan and Wings of the Goddess - then even with his Debit card details, which proved he payed SE a monthly fee, it didn't specify what it was for exactly or somesuch.