You Can't, Nor Should You
As was mentioned in the comments, you cannot prevent two adults from making the decision to divorce. However, given your current age and perspective, I think it may be helpful share some of my experiences to help you understand why divorce can be a good thing.
My parents divorced when I was 8 years old and at the time, I didn't really understand what was going on. What I did understand, though, was that my father was not smacking my mom in the other room anymore; nor was I being kept up at late at night overhearing shouting matches down in the kitchen. It was only later on in my life that I would come to learn about the concept of domestic violence and even later in life that I would learn to understand both of my parents' personalities and why neither of them are probably good marriage material.
Without delving into too many details, I will say that I learned that both of my parents were wrong. One may have been more wrong than the other, but it didn't change the fact that they both had legitimate complaints about the other and neither was willing to budge on these issues. As for why they married given these issues, I can't say, I obviously wasn't there when they were dating.
That said, I think there is A LOT of value in talking about your feelings in this situation. I caused myself a lot of unnecessary anguish growing up because I didn't talk about the confusion I was going through and nobody broached the topic because my parents' upbringing leaned heavily towards a 'bury your feelings' kind of approach to mental health (spoiler alert: this caused a lot of bad things for them as well).
You have indicated that you've tried to talk to your parents about this, but they didn't listen. I can only speculate that they may be at a point in this tumultuous time where they are unable to listen. It may be prudent to try and reach out to them at least a few more times to see if you can get through to express how you feel to them.
If that is not successful, I would recommend trying to write out your feelings, whether as a letter or just to put words on paper so that they're not stewing in your head. If you attempt to verbally speak with your parents several times, it may be prudent to try giving them a letter. Sometimes this cuts through the difficulties inherent in verbal communication and forces them to stop and think when they have the time to do so. I have done this before as an adult towards one of my parents, suffice to say, things got messy but did take an incremental step towards improving the situation.
Your question does not indicate the nature of your social circles, but if you feel comfortable confiding in a friend, I would recommend doing so. My recollection of the trustworthiness of other 13-year olds is based on information that's more than two decades old, though, so if you think this unwise then I defer to you on the matter.
Alternately, if there is a teacher or guidance counselor at your school that you trust, you can confide in them. Additionally, they may be able to reach out to your parents on your behalf if you're not getting through to them on your own.
Overall, I want you to know that when people divorce, it can be a good thing. It's far better to not be kept up every night because your parents personalities are just not suitable for living together.
However, these sorts of things do have fallout and impact the emotional and mental well-being of people close to the situation. For that reason, please do not neglect your mental health. Acknowledge and talk about your feelings with people you trust; if you have to cry take the time to. Bottling things up too long will hurt you in the long run as it did me.