I really had to quit
If an employer has created a hostile work environment you can make that claim. These are tough cases to win. But, if you have any chance of winning you must be prompt in your request for relief. Do not proceed to go this alone. You will need a lawyer to make a hostile work place discrimination case.
I decided to quit when told I'd be fired if I did not resign
If you resigned when you were threatened to be fired or else, then get it in writing that your employer is not letting you go because of "cause" and that your employer will "not dispute unemployment benefits". Without proof that you resigned only to avoid being fired, later your employer will challenge your claim and may come up with some "for cause" argument.
I did not call in but that does not mean I quit
Failure to communicate that you did not come in on a day scheduled for work can be deemed a constructive resignation. More and more, with all the pressures on the system for benefits, not calling in to report a valid absence is being deemed a resignation for which no benefits are awarded.
Retain an attorney
To go through the unemployment benefits appeal process, consider using an attorney for a consultation so you do not forget something or say something that compromises your rights. This is especially true if you are going to make a hostile workplace lawsuit. Good luck.