I bought a "as new" battery a few years ago from a RIBnet member. He promised me that he'd not used it as it was bought for a project that he never built. I paid me money and took it home. Was flat as a pancake so I tried charging it as you have done, just wouldn't hold a charge. Luckily he'd bought it from a local suppliers so i took it there for replacement, but they couldn't supply me as they had stopped stocking that make over a year before
They did however offer to ship it back to the manufacturers and that's how I found out what happened to it.
If you leave a discharged battery for a length of time then the plates inside get sulphate oxide on them. This ruins your battery and kills your battery for good.
My advice is to never buy a used battery and suggest you give the seller a chance of replacement or a full refund.