You do owe assessments from the date of the tax sale. You do not owe for the time before the tax sale. I would write back to the HOA and offer to pay them from the date of the tax sale forward. I would also let them know that if they sue you to foreclose based on debts from before the tax sale, you will pursue damages against them for an improper suit and/or improper foreclosure action.
All that being said, the issue is a little murky during the one year redemption period. The Court of Appeals has said you owe after the tax sale, but what happens if you pay the HOA and then the property is redeemed? I think you can argue that payment of the HOA dues was a cost to preserve the property, and you can get that back as part of the redemption price, but that is not absolutely clear. You can take a "wait and see" approach and wait until your redemption period is over and you bar the redemption, but that has the risk that the HOA would still come after you for the period between tax sale and redemption if the redeeming owner does not pay the assessments. If the home is covered by the Georgia Condominium Act or the Georgia Property Owners Association Act, the HOA cannot foreclose until they have a debt in excess of $2,000, and that would be from the date of the tax sale, not the old amounts prior.
The other murky issue , at least from the HOA's view, is that they may only be able to collect from you since the tax sale, but if the property is redeemed, the lien for the prior years, to the extent the statute of limitations has not expired on part of the debt, would reattach in the full amount.
If the association does file a lien for more than the post tax sale amounts naming you as the debtor, or if they file a suit, you will need to contact an attorney to defend the issue.
Hope this helps.
This answer is for general purposes only, and it does not create an attorney-client relationship.