$client = new SoapClient(
        'http://localhost/bgbilling/executer/ru.bitel.bgbilling.kernel.contract.balance/BalanceService?wsdl',
        array('login' => $login,'password' => $password)
    );

    $params = array(
        'contractId' => $contractId,
        'period' => array('fromDate' => '2017-05-01', 'toDate' => '2017-05-31'),
        'available' => false,
    );

    var_dump($client->balanceDetailList($params));