false advertising

I had a coupon for groupon that expired on the 30 november, when i messaged them, they said it valid for black friday only, when i noted their mistake of dates and it was valid untill monday 30th. they never responded to me and responded now on the 1st saying sorry it expired yesterday. I should still get that coupon as it was there mistake of dates. They responded a day late just to say sorry it is now officially expired.