The answer is you cannot celebrate or congratulate Christmas. now your Questions will be why not? Ok here is the answer. Christians celebrate Christmas on 25 December as they believe that Allah SWT gave birth (jana) to Jesus Christ Peace be upon him on this day Naozbillah. And this is Shirk biggest Sin in Islam.
Allah Swt says in Quran whoever says Allah has give birth to a child he has given biggest abuse to Allah Swt. Allah Swt also says in Surah Ikhlas Say He is Allah the one. Allah the Independent and Besought of all. He begets not, nor is He begotten. And there is none like unto Him.
Jesus Peace be upon him is Messenger of Allah Swt in Islam. So a Muslim cannot celebrate or congratulate Christmas to Christians. Because when someone says Marry Christmas he is actaully giving the Shahdah that Jesus Peace be uopon him Naozbillah is begotten son of Allah Swt. so instead of involving in it we should also do Dawah to Christians about it.