Magento – Cron job not running

so as a still-newbie I came across the task to write a cron job for our ERP, which is supposed to run at 23:45 every day and put stock data from a .csv into the shop.

I am currently trying to test it with it being done every 10 minutes (which also seems to be the set standard, more about the "seems" later) so that I can see what happens.

However, it doesn't seem to do its job. I'm also trying to parse some string into a .log but as nothing changes there, I can assume it's not working.

I've run the function manually and it worked, so no problem there (atleast it shouldn't be).

My guess is I have a problem with the names in my config.xml, but I can't figure it out.

I'm also using another self-written module which saves the orders, used for the ERP so they are in the same module. I will include them here.

paths

app/
    code/
        local/
            COMPANY/
                Erp/
                    Model/
                        Observer.php
                    etc/
                        config.xml

config.xml

<?xml version="1.0"?>
<config>
    <modules>
        <Company_Erp>
            <version>0.5.1</version>
        </Company_Erp>
    </modules>
<global>
    <models>
        <erp>
            <class>COMPANY_Erp_Model</class>
        </erp>
    </models>

    <events>
        <sales_order_place_after>
            <observers>
                <company_erp_model_observer>
                    <type>singleton</type>
                    <class>COMPANY_Erp_Model_Observer</class>
                    <method>writeOrderInfos</method>
                </company_erp_model_observer>
            </observers>
        </sales_order_place_after>
    </events>
</global>
<crontab>
    <jobs>
        <company_erp>
            <schedule>
                <cron_expr>*/10 * * * *</cron_expr>
            </schedule>
            <run>
                <model>erp/observer::updateStock</model>
            </run>
        </company_erp>
    </jobs>
</crontab>

file in app/etc/modules (COMPANY_Erp.xml)

<?xml version="1.0"?>
<config>
    <modules>
        <COMPANY_Erp>
            <active>true</active>
            <codePool>local</codePool>
            <depends>
                <Mage_Checkout />
            </depends>
        </COMPANY_Erp>
    </modules>
</config>

Observer.php

<?php

class COMPANY_Erp_Model_Observer {
    ...
    public function updateStock(){
        ...
        Mage::log('Cron job done!', null, 'company_erp.log', true);
    }
}

I know this is a long-a** post but I seriously don't know any further.

As I said, I don't know much about Magento, or CMS and stuff in general. I can work with them but understanding is a problem. I have no idea how to look whether cron.php is running on the server or not, but a co-worker said it is running. She tested it with "PuTTY" and said it runs every 10 minutes and writes the returns into nothing (null?), so I have a problem on my side.

I would appreciate any help or comments, as I do want to learn more. I like the structures in Magento but struggle very often.