Hello Everyone !
Here is exactly what happened.
I bought an account from @bartekssss which cost like $17 in PayPal , The account was unregistered. I have sent to him the money to his account and he had received. He sent to me the tibia account. When I received , I changed the password and the email address of the account but i didn't register the account because I wanted to lvl it up and sell it (since unregistered accounts are more valuable than registered) . After i changed the email address and password (Note that the e-mail address will be unchanged only after 30 days) I slept. The next day when I tried to log into that account , It was saying invalid account name or password. I tried several times to login but I couldn't. Then I contacted the him for help or refund, he refused to refund the money and he claimed that he didnt change the password. I tried to open a dispute in PayPal but that didn't help.