Verified answer

Almost every person who wants to learn a foreign language has this problem.This is because when you learn Greek,you learn the Greek as language but in Greece people speak more natural than the typical Greek language.If you want to speak perfect Greek you need to stay for a while in Greece in order to speak the language every day.Also,if you mean that your friends on Facebook speak greklis(Greek with english alpabet)there is no problem with your Greeks.I live in Greece for almost 13 years and i can't understand people who speak greklis.So don't worry.Just tell them to speak one language,Greek or English.Only then you will understand.

You are probably learning the "proper" form of Greek. Think of it as the difference between proper, eloquent English, and the way you might speak with your friends. Also, there are usually slight differences in a language in different regions.

many greeks use latin alphabet on the internet (facebook, youtube) because they are bored to change the keyboard language from EN - Greek everytime.

it happens to all languages

there is the formal version that is tought and the "street" version that people talk in their daily lives.

Street version can only be learned from experience