Understanding recursive function in linked-list C

Let's suppose I write a program that simulates the Dominoes game, so I'd like to define a struct the following way:

typedef struct nodo { 
    int casella1;
    int casella2;
    struct nodo *next;
} Tessera;
typedef Tessera *Lista;

And then after some input in casual order that ends when a number outside the range 0 <= x <= 6 is entered, I'd like to delete the possible duplicates that don't respect the domino rules. The number casella2 should always be succeeded by the same number in ->next->casella1, using a recursive function, that goes like this:

void legale(Lista *head) {

    Lista aux,aus = *head;

    if(aus->next == NULL) {
      return;
    }

    else if(aus->casella2 == aus->next->casella1)   {
      legale(&(aus->next));
    }
    else {
      aux = aus->next;
      aus->next = aus->next->next;  
      free(aux);
    }
}

But for example the sequence " 1 2, 2 3, 3 4, 4 5, 5 4, 6 2, 7" gives "1 2, 2 3, 3 4, 4 5,6 2 " So it doesn't delete 6,2 as it should.

I think the way I deleted the pointer is correct, so why is the function wrong?

The code goes like this :

#include<stdio.h>
#include<stdlib.h>
typedef struct nodo { 
    int casella1;
    int casella2;
    struct nodo *next;
    }Tessera;
typedef Tessera *Lista;

void stampa(Lista *head) {

    Lista ausil = *head;

    while(ausil != NULL) {
    printf("%d\t%d\n",ausil->casella1,ausil->casella2);
    ausil = ausil->next;
    }
}

void legale(Lista *head) {

    Lista aux,aus = *head;

    if(aus->next == NULL) {
    return;
}

    else if(aus->casella2 == aus->next->casella1)   {
    legale(&(aus->next));
}
    else {
    aux = aus->next;
    aus->next = aus->next->next;    
    free(aux);
}


}

void write (Lista *head) {
    Lista corr,aux,aus;
    int x,y;
    scanf("%d%d",&x,&y);
    aus = *head;

    while((x >= 0 && x <= 6) && (y >= 0 && y <= 6)) {

    if(aus == NULL) {

    aus = malloc(sizeof(Tessera));
    aus->casella1 = x;  
    aus->casella2 = y;
    aus->next = NULL;
    *head = aus;
}
    else {
    aux = *head;

    corr = malloc(sizeof(Tessera));
    corr->casella1 = x;
    corr->casella2 = y;
    corr->next = aux;
    *head = corr;
}
    scanf("%d%d",&x,&y);
    }

}

int main() {
    Lista Lista1 = NULL;
    write(&Lista1);
    legale(&Lista1);
    stampa(&Lista1);
return 0;
}