@Seb *******
an embassy/consulate (especially one that issued eVisa) can't cancel an extension OR a visa issued by another consulate (that was totally b/s from the consulate)
There are many reports of people who weren't sure they were going to get the DTV issued keeping their current extension buying a re-entry permit going to a thai consulate to get the DTV and then telling passport control when they stamped in that they want to get stamped in on the DTV.
After they got back they went to the immigration office where they got the extension and cancelled it without issue