Not Issued Handstamp On Postage Dues

I have no idea what that means on this cover from Dec 12, 1977. The stamp under the pair of one cent stamps is another three cent, with the same handstamp.

No matter what I do, I cannot get the image to upload. I have adjusted the size, I have read the tutorial, but it just won't load. The green arrow just gives me the image n my pc.

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I leave that for you. This cover has 16 cents postage due with a red NOT ISSUED handstamp over some and some others on top with normal cancels. I sent an image on to someone hoping they can post it, since I am ready to throw the PC out the window at this point.

Here is the image in question:

Thank you.

Looking at it carefully, it seems to say 11 cents due, had 11 cens in stamps marked with the handstamp, then 13 cents added. Strange.

Three days from San Francisco to North Carolina, normal for back in the good old days.

Someone at Gibsonville wrongly affixed 11¢ in postage due stamps before the 11¢ was collected, then realized the error and marked the stamps NOT ISSUED.

Box clerk left notice for addressee to come to counter and pick up the mailpiece and pay due postage.

Addressee came over and paid, and new stamps were added to receipt the payment (and to keep the clerk's drawer of stamps and cash in balance) and were postmarked / canceled.

Looks like 11+11 to me.

Normally one sees multiple sets of dues on letters taken out for delivery and which failed, and then one sees a "VOIDED" handstamp on those dues not actually collected and returned by the carrier for credit. In this case they used a device which achieved the same accounting purpose, but might be more proper to invalidate an unissued money order or similar accountable form/item.

Unusual in this case, the letter is addressed to a PO Box, so having no need to leave the post office for delivery attempts. One would simply expect a note to be left in the PO box and the letter to sit at the PO until called for, requiring only a single set of dues to achieve the purpose. (Agreed with Mike posting simultaneously, that the dues to be applied at the time of collection for box mail, not before.)

It is 11+11. Which brings up the question of why it is not 13.

Was there a special 2 oz rate?

13 for the first ounce 11 cents for additional ounces.
See the Beecher/Wawrukiewicz rate books.

This is one of the rare times when I have an interest in a postal rate. I have the books for the revenue rates for 1862 and 1898, which I use fairly often.