In order to check your check your company`s GLN, you can use official GS1 website and choose Search by GLN:

Please note:

If entered GLN is not linked to your company or it is not registered the message below will be shown:

If entered GLN is correct, the respective fields below will be filled in with your company details:

In order to check your company`s GTIN, you should choose Search by GTIN:

Please note: 

If entered GTIN is not linked to your company or it is not registered GS1 will correct the wrong checkdigit  and the message below will be shown:

Even if you re-submit the form the page won't display the information about the product or your company because that GTIN number is not registered for your company. 

If entered GTIN is correct, the respective fields below will be filled in with your company details. 

GTIN has to be linked to your company`s GLN