Does the person redieving a bank notarized letter have to comply to letter notarized?

i verbally expired my rights of 6 years as my sisters power of attorney.. i helped her win her custody battle being her accident left her a quadriplegic..i verbally expired my rights back in 2009, then this year 2011, she had someone type a letter in relieving my poa duties..she then added that i had no ability or rights to inquire about her two children is this something legal? or is this a request ? i dont no.. the delivery was sent regular mail not certified, not from court or attorney..what does this mean?