icloud lock
My problem is next : i have bought second hand iphone 4 with box (so i don't think that iphone is stolen) he said that iphone was running properly before he had done downgrade after that icloud locked his phone and itunes ( now ) requires to activate iphone and someone's apple id on which was iphone setuped first time ( i think he lies me, i think he bought from ebay or etc. icloud blocked iphone) and shows first letter and @yahoo.com (m*****@yahoo.com) he didn't know this full email or password (because i think he bought from ebay or etc icloud locked and it was setuped on someone's apple id). itunes requeres activation BUT when i reset all contents and settings iphone only switch off and i have erased iphone, problem is that iphone didn't require set up from iphone, it switchs on simply without set up region, language and etc ( i didn't understand why) can you tell my why ? my iphone 4 is gsm and was blocked with AT&T carrier (before i bought) and prewious owner (or first idon't know) factory unlocked iphone and when i check iphone with imei (when i do imei check) it's written unlocked BUT find my iphone is on (when i can turn on or off by iphone find my iphone) but i think into system find my iphone is turned on.
i have all this questions :
1. why no service ?
2. why i can't update ios ?
3. why i can't set up iphone from iphone ?
4. could i search anywhere prewious (first) owner's mail on whitch was setuped iphone first time ?
5. will downgrade help me with this problem (downgrade from ios 7.0.6 to 4, because ios 4 haven't icloud)
6. how can i turn find my iphone from system (to imei check write me that find my iphone is turned off) ?
7. where coul i see full e-mail of previous owner ? to contact with him
i will be very surprised and pleasured if someone help me. thanks and sorry for mistakes in language. thanks
iPhone 4, iOS 7.0.3, 32 gb