How many days do I have to leave Thailand after my BOI visa is cancelled?

Howdy all,

I was hoping someone could help with a question regarding a BOI visa cancellation...

I'm leaving a job at the end of the month and for whatever reason I always thought I had 7 days to get out of the country once my current visa gets cancelled. However the lady taking care of our "visa stuff" has just come back with this statement;

"usualy non Immigrant can extend 7 day but we have visa by BOI, So BOI give 15 days. Totaly 15+7=21 days."

Is anyone up to speed with BOI and can confirm this 21 day extension of stay upon visa cancellation?

I've had some, a'hem, missinformation from local "visa stuff" staff in the past, so was hoping the learned members of this group might be able to confirm if this 21 day thing is legit.

She's not asked for my passport, so I'll have no visual record/stamp of the visa being cancelled in-country. I guess the BOI multi-entry stamp in my passport just gets flagged on the network/systems at immigration once I try and exit at the border (which also smells a bit fishy IMHO).

Any insights or experience in this area is much appreciated.