Hello Pelin! I tried to call you, but your phone was disconnected. correct!

Both are correct but mean slightly different things. "I tried to call you, but your phone is disconnected" means the telephone company have disconnected their telephone line (or mobile link) and at the time of writing or saying this phrase the phone line is still disconnected. "I tried to call you, but your phone was disconnected" means that at the time you made the call the telephone company had disconnected the telephone line but now it has been reconnected. To use "disconnect" this means the telephone company has made the disconnection, if it is the phone user who you wanted to call who has turned off their phone you would say: "I tried to call you, but your phone was off." or "I tried to call you but your phone was on divert (to voicemail)". Also if you tried to call but the other person was already on a call you'd say "I tried to call you, but your phone was engaged" Hope I haven't caused too much confusion.