"Per" is a pronoun. Always say "me" after a pronoun. Use "mi" right before a verb: "mi dice che" "he tells me that...." Use "me" before another another pronoun before a verb. "me lo dice" "he says it to me." Use "me" after a verb for emphasis. "mi odia" "he hates me" but "odia me" "he hates ME." Sorry it's so complicated.
"Lei" is the direct object form and is used for the object of prepositions. "Le" is an indirect object form. "Le dico la verita'." "I tell her the truth." It's also a plural form: "Le vedo" "I see them (feminine)." So you have to say "per lei." Confusingly "lei" is also a subject form, while the subject form of "me" is "io." I'm starting to confuse myself.
Here scroll down here for the tips and notes: https://www.duolingo.com/skill/it/Clitic-Pronouns-1 "la" is the direct object form, "le" is the direct object form and "lei"is the tonic/disjunctive form which can be used anywhere in the sentence, including after prepositions, and is used for emphasis when used in place of the direct or indirect object forms.
You are right though, "me" and "te" are just not used as subjects, are they? You are already creating emphasis when you include the subject pronouns "io" and "tu" since the verb form already implies the subject.
The reason the direct and indirect forms are called clitics is because they can stand in front of the verb or become attached to the back of a verb.
Ti telefono da Roma.
Scroll down here for the tips and notes: https://www.duolingo.com/skill/it/Clitic-Pronouns-1