change of address

i called Mtn on the 11 and the 12th to request address on my account to be changed and to get my invoice with the new address on the 13th, today the 14th received invoice with my old address.<br> how hard can it be to change a simply request its not like i was asking for the world i need the letter to reflect with my new address as i'm applying for library cards for my kids. i would understand if they gave me a follow up date with changes but she did not advise that has been changed.