Hi, I would some advice please re how the combine shipping works. I purchased two small plants off a seller. I added to cart, then selected "Rural" for one ($16.40) and then "Quote for Combined Shipping" for the other. I then paid the total requested, which was just the $16.40 shipping for the two. I got the confirmations, all good. Then later the seller emailed to ask for more shipping, saying the total is $24.60. Maybe I am misunderstanding here, but I thought I had paid for Combined Shipping. I can't find any info on this. Can someone please advise. Thanks