It needs to be more than within the 7 days, though. You need to notify them that, in a permanent for (i.e. not by phone) that you are cancelling the order .... i.e. in the words of the DSR "give a notice of cancellation".
Does requesting an RMA, even if you did it in writing, by mail, email, fax. etc, constitute "cancellation"?
I'm afraid I rather doubt it, at least under some circumstances. If you organised an RMA for a
replacement, or alternative goods, then it's hardly cancelling,
IMHO.
Are you still within the 7 days, bearing in mind that's
working days (excluding weekends and bank hols),and starts the day
after you receive delivery? If so, get in a cancellation letter or equivalent, right quick. Oh, and for clarity, it's the fate you
send that notice, not when it's received, that has to be within the 7 days, so if you do it by post,
get proof of postage as it's that date that matters.