1) Use "can" here - once you receive the information, you will be able to ("can") issue the refund. "Could" would be used if it were phrased as a conditional: "If you were to send me the information, I could issue a refund" - receiving the information would make you able to issue the refund. 2) "on our website": the preposition "On' has become the one to use. I don't think there is a British/American divide. It has a certain logic: we look at websites on a screen, and movies and TV broadcasts are already described as being "on the screen". It also parallels the prepositionalphrase "on the internet". You would, of course, say "at our store" if referring to a physical store in the real world. I suppose there are still people who might wish to imagine the internet as a virtual "space" and might want to "humanize" things by making a website sound like a store by saying "at our website". But I think the language has more or less settled on phrasing it as "on our website". One interesting prepositional divide concerns the verb phrase "waiting in line". New Yorkers will say "waiting on line" (to buy tickets, pick up a prescription, shake a celebrity's hand, etc). Everyone else in America says "waiting in line"! This has become a little confusing now that we also have the term "online". 2b) Other ways of phrasing this? "as noted on our website", "as detailed on our website", "as explained on our website" perhaps?