' baby mama is calling BS on the ex-NFL receiver after he claimed she blew $4 MILLION on drugs ... telling TMZ Sports, "I've been clean for years."
Moss called out his ex on Twitter last month ... claiming the mother of his 5 children refused to get treatment for a drug addiction in order to see her kids.
We spoke to Libby Offutt ... who says Moss' allegations are completely untrue and an attempt to keep her from seeing her children.
"I went to rehab TEN years ago and have been clean ever since," Offutt says.