Can't confirm the payment?

I buyed BTC and payed the money and confirmed the payment.
After 2 days the seller send me a small payment back to tell me, (over the payment reason) that he got the money but can’t give me the BTC, because I need to authorize the payment.
But I already did it.
What I should do? (I don’t want to lose the sec deposit)

Open a dispute (cmd+o or ctrl+o). You will not lose the sec. deposit if all was correct. Only clear violations of the trade protocol leads to loss of the security deposit.

Just want to say that I confirmed the payment. Probably a bug.