I wonder if something was wrong with your mail delivery. Are you sure that your mail arrived on August 2? The final date for receiving H1b petitions was August 10. If yours was before that time, there would be no problem. And generally you should get the receipt in one or two days after USCIS gets your petition. The only explanation about your case was that they received your petition after August 10. If that's not the problem with their service, there must be something wrong with your delivery.