Sorry to hear about your problem -- but we need much more information.
Is the freeze during recording or playback?
How long does the freeze last if you didn't reset the main unit?
How many dvr's do you have?
Do you have a Genie setup?
Does this happen when you are watching something not recorded?
Have they checked your satellite dish?
Does this occur during bad weather, or is it during mild weather?
Additionally, you can call DirecTV back and tell then a tech was out but couldn't find anything. Now, you want to have this escalated to someone who can help you.
I have found DirecTV to be VERY accommodating if there is a problem and they will do everything and anything to retain you as a customer. Their customer retention customer service department is extremely conscientious. They do NOT want to lose you as a customer.