Product short!

I have purchased the 337g Lindt assorted Silver edition through Sixty Sixty. The sealing stickers were in tact. The box felt light so I have weighed it. It weighed 290g with the box. I have sent them an e-mail and they have told me to return it to the store from where it was purchased. In the end I have opened it and there were only 20 chocolates in the box. Also no choc and white that was supposed to be in the box. As it was an online purchase I cannot return it to the store. No voucher, no nothing. My loss!!!!