Hello hope this helps
If you are asking a friend to repay a debt, generally we use "reclamar" because you are asserting your right to something owed to you in an casual or non-legal context
Secondly - when canceling your order, "reclamar" is still appropriate if you are making a request ti resolve an issue or claim something back {e.g a refund}, however you wouldn't use "demandar" unless you are threatening or pursuing legal action