Most people would say anasta-ZEE-a. The name is rare but well-known in Germany and especially used among people of russian descent.
Like elbowin said: There is also a dialect in Germany where the -st- is always pronounced sht, even if you would say s-t in High
German (e. g. the word "weißt" or popular
German names like
Konstantin,
Christian ...).
On the other hand, there is a North
German dialect in which -st- is always pronounced s-t, although in High
German it is sht (e.g.
Stein,
Stephanie ...).