Im calling this girl and shes not picking up ...but i want to tell her a few things what can i do?

weve been going otu for a while and crecently has slowly started to lose intrest in goign out and even lately is not pciking up her phone..after a week gap..i called again and she didnt call back...but i feel liek iwant some kind of closure atleast or an explantion...what can i do?? email her? text her? what should i say?