Communicate in writing via fax or email and make your letters polite courteous and professional. Make them self serving confirmong the extensions and courtesy you have extended, and their unreasonable refusal to accomodate you when there is good cause. Then you may have to go to court on a motion. You will have written proof of your attempts to work it our w/o wasting the courts time. Perhaps the atty wont want to look bad in front of the judge.
The advice in the prior answer is sound.
While professional courtesy is far and away the better practice, it is not always given. There is no rhyme nor reason to this, and much depends on the personalities and training of the people involved. All I can tell you is that I have had similar exchanges with opposing counsel, and your experience is not necessarily a reflection on the fact that you are pro per.
Best of luck to you.
However, it really does help to have an attorney. Unfortunately many attorneys feel they can get away with things when an I represented party is involved. Good luck!
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