Can I block my iPhone if it's with someone with their Apple Account in it?

Hello, I bought a phone 6 months

ago, which I gave to my friend

to use for a period of time,

during which she created

an iCloud, and later when

I asked her for it back

she didn't give it to me.

I want to ask what to do

in these circumstances,

in which the phone

was bought through a

Romanian telephone

company (Vodafone)

and I still pay a

monthly installment

for it. Can I still

get it back? I want

to specify that she

has both the phone and the

box. I can prove the

payments made from

the beginning on it by

bank transfer or invoice.

I am interested in

temporarily blocking

the phone until I get

it back, and I understood

that only if I talk

to someone from you can

I do this. Thank you

very much and I await an answer.

[Re-Titled by Moderator]