Since english is not your native language, it's a bit hard to understand what you wrote.
It looks like you bought something using bitcoins, and the seller claims that you did not send the bitcoins to him.
There are several possibilities:

• The seller did indeed receive your bitcoins and wants to cheat you.
• The seller has some technical or understanding problems and does not see the bitcoins you sent to him.
• You sent the bitcoins to another address than the one given to you by the seller, either
   
  • ... because you misunderstood something in his message
  • ... because your computer is infected with a trojan that replaces bitcoin addresses by criminal's addresses when you make a transaction or when you receive a message containing an address

Which of these might have happened is impossible to say without much more information.

Onkel Paul