Am I overreacting/overthinking my relationship with my girlfriend and her ex-boyfriend?

To make a long story short, I been with my girlfriend for four months. Its been a crazy four months because three days in our relationship I caught her in a lie. She told me that she went to Savannah for mothers day, which was a lie she was still here in Atlanta. Plus she told me that she did not talk and had her ex-boyfriend blocked again a lie. She still follows him on social media and has talked to him via text. She has told me that its over with him and will never get back with him. This past weekend I got a letter with my address labeled with his name, I asked my girlfriend why is a letter eith her ex-boyfriend name in my mail box. She said its from a free phone she got from the government. Last night my friend sent me a ig post with her ex-boyfriend talking and in the background you can hear a woman talking and laughing. The voice to me sounds like my girlfriend, i have been around her enough to know how she sounds. The main question is what should i do, because all i have is a video with a voice no face. She called me insecure about this situation with her ex. Am I over reacting or should i be worried.

Am I overreacting/overthinking my relationship with my girlfriend and her ex-boyfriend?
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