The Wedding RSVP

I received a wedding invitation for a 'destination wedding' on the opposite coast.  I have only met the bride and groom once (I am a casual friend of the bride's mother).  The wedding invitation was, shall we say, non-traditional and wanted the RSVP online along with instructions on how to contribute to the gypsy van motor home the couple wishes the wedding guests to purchase for them.  If the motor home option was not something the guests wanted to do, they requested cash and gift cards only as their small apartment can't accommodate "stuff."

Somewhat insulted that the bride and groom, to whom I don't have any attachment and could not identify me in a police line up now demanding cash, I did resist the temptation to reply with snark and dog shit.  I did send a hand written card sincerely wishing them well, sending our regrets, and a check.  I did this for no other reason than out of respect for the bride's mother as she is a lovely lady.

I have now received a mass produced 'nagging email' saying that I have yet to RSVP to the wedding.  I did.  I sent a personalized response via US Post along with their wish for cash.

It then dawned on me that perhaps they did not receive my card/check.  I emailed the bride asking her if she received my card as it enclosed a check and my hand-written regrets.  If not, perhaps I should put a stop payment on the check and reissue another one.  I have yet to hear from the bride and it's been a few days.  I have no other way to get a hold of the bride except through their wedding website and email address.  Do I approach the mother?  Should I put a stop payment on the check and drop the matter?

I'm trying to act in a dignified matter despite the crude, obvious, impersonal, and opportunistic on-line cash grab of near strangers.  I suppose my crime is trying to make a personal connection to an impersonal invitation/request for money.  Guilty.