I don't understand your response. I suggest you stop being defensive and make an appointment to talk with the appropriate person at the school about this issue while keeping an open mind. The person who called you is the person with whom to start. Call and tell them that you do not understand the policy and ask to make an appointment.
Before going to the appointment observe other students before and after school to see if in deed other students are wearing jeans with holes in them. Do not just take your daughter's word for it.
Recognize that it is important for your daughter to learn to follow the rules, even when she doesn't agree with them. And show your daughter that you respect authority and their right to make and enforce rules. Also show her the appropriate way to go about changing rules when changing the rules are important to you. .
When making the decision of whether or not to work towards change, consider the amount of time and energy you have to give to trying to make change in comparison to the likely amount that it will take. Always model respect for the rules in place and for the authority that enforces them as well as respect for yourself and your daughter.
Let go of your anger and defensiveness. Hear both sides before making a judgement. Apparently you have decided that the school is wrong. Let go of that decision and start over. When we talk with people in anger and with an already decided opinion we get nowhere. An open mind and a calm manner will solve almost any situation.
Another focus: I would ask why your daughter was caught. If the hole is as you described something else happened to bring attention to her. I suggest that the possibility that the "real" problem is not the hole in the jeans.
An aside: I'm 67 years old. When I was a senior in high school the dress code said that girls could not wear patent leather shoes and that their skirts had to be below the knee. Pants in any form were not allowed. One day a popular girl came to school with her skirt hemmed to a point just above the knee. She was told to either take the hem out or go home. She took the hem out. I was irritated, thinking the length of her skirt was not important. My mother said that teens have to rebel in some way in order to become a separate individual and go on to become adults. It's better to rebel about the length of their skirt than about many other things such as drinking alcohol or having sex.
This idea is over simplified but it does illustrate the importance of having rules to help teens form boundaries that will enable them to have success as adults.