Filling a 2D Array with Random Letters - C Programming

So in the previous thread I wasn't clear about the issue and I posted a lot of code.

I'm totally new to C Progamming and I encountered some issues.

I'm trying to create a Word Search, however I encountered a problem.

I'm trying to fill the Word Search Grid ( a 2D array) with random single characters) (Characters like A,B,C,D,E... )

I'm trying to use the rand() function , however I can't get it to fill the whole 2D array. When I'm trying it I only can get it to fill the first slot.

This is the code where it fills the puzzle. At the moment I filled with with '.'

void createBlankPuzzle()
{
    int i , j;

    for(i = 0;i < ROWS;i++)
    {
        for(j = 0;j < COLUMNS;j++)
        {
            puzzle[i][j] = '.';
        }
    }
}

I'm trying to generate the random character with the rand() function.

char getRandomCharacter() 
{
    int rl = (rand() % 26) + 65;

    return (char)rl;
}   

I hope this is clear enough and I tried to use good formatting.