Groupon and EastWest Bank overcharge Mystery

I purchased a Shi Lin voucher on Groupon Philippines using my EastWest Dolce Vita Mastercard credit card.

Then I chose to pay 500 pesos for P1000 value. The credit card payment system stated that I will pay 500 pesos for the transaction. I entered my credit card details and confirmed the payment. The transaction was successful and I received my voucher.

When my statement of account from EastWest bank arrived, I am a bit confused on why did they charge me 512.50 pesos. Isn't it supposed to be P500? I know that 12.50 is a small amount but I don't like that they made a mistake.

I contacted the Groupon customer service via the posted link on their contact section (Sorry, I forgot what my inquiry is ^^ It's sort of I inquired them where the excess charge came from).

What I like about their service is it doesn't take several days to reply and answer your inquiries. They answered within the day I emailed them.

I even registered to their Groupon Philippines Zendesk to track my queries.

Here's the trail after I sent my inquiry:

Received an auto mail after I sent my inquiry

A representative answered my inquiry:

• Hi Ms ----------,
  Thank you for the email.
  In regards to your concern, we actually received some emails regarding the eastwest credit card overcharge which some of the bank did not, so we can refund it or put the excess charged to your groupon credits which can be use for your future purchases.
  Please advise if you want to proceed.
  Let me know if you have further inquiries.
  Thanks,
  ------------
  support@groupon.ph

Me:

• I would like to proceed for the refund. Regarding the groupon credits, will the credits expire if you put the excess charge there?
• 
  
  

There's no answer after this. After a day or two, I checked my account and 13 pesos was refunded to my account. After three days from my last inquiry above (a bit late actually), the representative made a reply.

• Hi Ms ----------,
  Thanks for your email.
  I've just have requested that Php13.00 Groupon credit be put on your account.
  The credit is available at the end of the working day and is valid for 12 months. You can see your available credit in the "My Credits" drop down found by clicking "My Account" on the top right hand side of the screen once logged in. Make sure you tick "Use Your Credit" when checking out to use your Groupon credit.
  Please enjoy and let me know if I can help you further.
  Thanks,
  ------------
  support@groupon.ph

I am glad that my problem was solved but my questions on my mind are: How about if hundreds or thousands are wrongly charged on the purchase? Will they refund it to your credit card account? Who made a mistake? Is it Eastwest Bank or Groupon Philippines?

I hope they will fix these kind of issues if they already received emails concerning this credit card.