Query by table text using PDO

Question

My seemingly simple problem has given me headaches. I have a table that contains three columns: id, idpergunta, resposta. When a reply is sent to be inserted in this table I check if it already exists:

$where = [
            1 => $resposta['idpergunta'],
            2 => '' . $resposta['resposta'] . '',
        ];    

        return count($this->db->select("SELECT idresposta FROM resposta WHERE aberta = 1 AND idpergunta = ? AND resposta = ?", $where));

The method select is implemented using PDO as follows:

public function select($sql, $array = array(), $fetchMode = PDO::FETCH_OBJ, $class = '')
    {
        $stmt = $this->prepare($sql);
        foreach ($array as $key => $value) {
            if (is_int($value)) {
                $stmt->bindValue("$key", $value, PDO::PARAM_INT);
            } else {
                $stmt->bindValue("$key", $value);
            }
        }

        $stmt->execute();

        if ($fetchMode === PDO::FETCH_CLASS) {
            return $stmt->fetchAll($fetchMode, $class);
        } else {
            return $stmt->fetchAll($fetchMode);
        }
    }

However, the way it is, if the text of the answer is larger than two words it does not find it. Sometimes it works and sometimes it does not. I’ve tried several ways, but nothing solves it. Time works, time doesn’t work. What could be causing this? I am absolutely sure that the data is correct. If I do a query manually on the server the return happens normally.