Time limit to return ESA form

My ESA form arrived to today. I am prepared and ready to give the best account I can with the aid of Benefits and Work handbooks. The one thing that bothers me is the time limit to return the form. I was told that you will have 4 weeks to return the form when really speaking its only 3 weeks.I have to get as much much evidence and support letters together and to get the form back to ATOS by the 8th August. The problem is that most of the health officials I need to see are either on holiday two weeks before or off sick. The 8th is on a Wednesday,so to allow plenty of time for the form to arrive at ATOS I need to send it either the Friday/Saturday(registered post)But I how can I get any support letters?I know I can send them later but I think I would stand more of a chance sending letters with the form. I rang ATOS and asked for an exstention and I was told very firmly that 4 weeks is quite long enough to fill the form in.
Also,on the forum two weeks I put in a post about incoming calls. I had to phone the DWP telling them about my new phone number and she said that while I was on the phone she will go though any details and put a note saying that I won`t be called again.
The following week I got a call from the JOBCENTRE plus regarding the follow up call to the letter I received when I told them I had already given details,she replied there was no record of that call. There must have been,how did they get my new number? She ask me different questions to the other one and she asked me three times for my postcode and three times for my marital status. When asked if I had any questions,before I could say anything,she put the phone down.Was there any need for two calls?