Problems with being granted a PIP extension

Hi! I'm new to the forum. I've searched through the topics and can't find an answer to my concern hence raising it here. My PIP form didn't arrive so I contacted DWP who sent another. The deadline date for the form is 12 Sept. Due to increased severity of symptoms (relating to disability) and needing assistance from family to help with the completion of the form ... I finally got through to someone at DWP today. I explained the situation and asked if I could have more time (extension) to complete the form. I was told that I'd already had one (which isn't the case) and explained that I hadn't received the first form but did receive the second one that had been sent which has a deadline date of 12 Sept. I was told that the case manager (?) would call me back this morning but I didn't hear anything. I will try again tomorrow. I'm not sure if there was a problem with how the current form was logged on to their system (as an extension rather than replacement form) or whether it's something else. Has anyone else had this problem? It's extremely tense because the deadline is looming. Is there any key advice when I call back? Many thanks for any advice and support.