how to delete flat table custom model object with foreign key?

Created flat table model that have foreign dependency for customer_entity.customer_id column, and for some unknown reason I am unable to delete object that I have successfull created before:

                 $required_model = Mage::getModel('Mymodule/Payments')
                    ->getCollection()
                    ->addFieldToSelect('customer_id')
                    ->addFieldToSelect('email')
                    ->addFieldToFilter('customer_id', $session->getCustomer()->getId())
                    ->getItems();

                if(is_array($required_model) && (count($required_model) > 0)) {

                    try {

                        reset($required_model);
                        Mage::app();
                        Mage::app('admin');
                        Mage::setIsDeveloperMode(true);
                        $model = $required_model[key($required_model)];
                        $model->delete();
                        var_dump($model); // object does not delete from table, and succesfully var_dumps here
                       }
                       ...

var_dump succesfully dumps the object:

                    object(Mycomp_Mymodule_Model_Payments)[175]
                      protected '_eventPrefix' => string 'core_abstract' (length=13)
                      protected '_eventObject' => string 'object' (length=6)
                      protected '_resourceName' => string 'Mymodule/payments' (length=12)
                      protected '_resource' => null
                      protected '_resourceCollectionName' => string 'Mymodule/payments_collection' (length=23)
                      protected '_cacheTag' => boolean false
                      protected '_dataSaveAllowed' => boolean true
                      protected '_isObjectNew' => null
                      protected '_data' => 
                        array (size=2)
                          'customer_id' => string '215' (length=3)
                            ...

my module config.xml:

            <mymodule_resource>
                <class>Mycomp_Mymodule_Model_Resource</class>
                <entities>
                    ...
                    <payments>
                        <table>mymodule_customer_payments_info</table>
                    </payments>
                 </entities>
                    ...
            </mymodule_resource>        

resource, collection and model files are set and initialized in constructor

where to dig ? thanks!

ps:

teble skeleton is like this:

    try {
        $sql = "
          CREATE TABLE `{$this->getTable('Mymodule/payments')}` (
            `entity_id` int(10) unsigned NOT NULL auto_increment,
            `country` text NOT NULL,
            `email` text NULL,
            `vat` text NULL,
            `customer_id` int(10) unsigned,
            `type` int(10) unsigned,
            `created_at` timestamp DEFAULT CURRENT_TIMESTAMP,
            PRIMARY KEY (`entity_id`),
            CONSTRAINT `FK_mymodule_customer_payments_info_customer_id` FOREIGN KEY (`customer_id`) REFERENCES {$this->getTable('customer_entity')} (`entity_id`) ON DELETE CASCADE ON UPDATE CASCADE)
          ENGINE = InnoDB;";
        $this->run($sql);
    }