as said above めっちゃ has the meaning of very, extremely etc. めっちゃめっちゃ is just emphasising that even more. this word is more commonly used in the west of japan such as in the Kansai dialects and I have also found it used in the Tosa Dialect (currently learning this one).

As Karumu said, めっちゃめっちゃ means 'very' and that's a Kansai dialects. I lived in Osaka and めちゃめちゃ is very common word. e.g.) めちゃめちゃ寒い is "it's very cold".

めちゃめちゃ的本来的意思是非常杂乱， 但是作为副词是非常的意思。 是中性词，好的，不好的都可以搭配。但是有限制，是年轻人口语中常用的词。

めっちゃめっちゃ is really or very so めっちゃめっちゃ美味しい is delicious or very very nice