Annotation:
"Not buy it" is an idiom.
https://www.google.com/search?q="not+buy+it"+idiom
It means not to believe it's true.
Related:
[#3008752] I'm not buying it. (CK) *audio*
[#3150398] I'm not buying it, Tom. (CK) *audio*
[#2545905] I'm still not buying it. (CK) *audio*
[#3150391] Tom is just not buying it. (CK) *audio*
[#3150408] But I'm still not buying it. (CK) *audio*
[#3150411] Actually, I'm not buying it. (CK) *audio*