Sales records should not be dialled again

Hi,
In one of my campaign phone number is the primary key to sell. If agent sold on one telephone it should not be called again within the campaign. Problem which I am having at the moment, once agent disposition one record as a sale if someone else manually dial the same record system allow to dial. Is it possible to stop this, once lead is dispositioned as sale record should automatically be marked as DNC for that campaign.
Best regards,
In one of my campaign phone number is the primary key to sell. If agent sold on one telephone it should not be called again within the campaign. Problem which I am having at the moment, once agent disposition one record as a sale if someone else manually dial the same record system allow to dial. Is it possible to stop this, once lead is dispositioned as sale record should automatically be marked as DNC for that campaign.
Best regards,