return from function changes value of array element in c

I am trying to implement a function which fills a struct, including an int array[3][31]. Inside the function everything is fine but when I return a pointer to my struct and print it out in the main function the elements [1][0] and [2][0], which should both be 0, are 32 and 4.

I already went over it with the debugger but the values just change as soon as it leaves the function.

Here are the relevant parts of my function:

struct monat* create_monat(int zahl_tage, int erster_tag){    int wochen_tage[] = {1, 2, 3, 4, 5, 6, 7};    monat* neuer_monat = malloc(sizeof(monat));    int count =0;    while(neuer_monat->kalender[0][count] !=2){        int wochen_tag = wochen_tage[(erster_tag-1 +count) %7];        neuer_monat->kalender[0][count] = count+1;        neuer_monat->kalender[1][count] = wochen_tag;        if((wochen_tag == 7) || (wochen_tag == 6)){            neuer_monat->kalender[2][count] =1;        }        else{            neuer_monat->kalender[2][count] =0;        }        count++;    }    return neuer_monat;}

And I am calling it with this

int main(){    monat* jan24 = create_monat(31, 1);    for(int i=0; i<3; i++){        for(int u=0; u<31; u++){            printf("%.2d ", jan24->kalender[i][u]);        }        printf("\n");

Can somebody help please?