I also was once Pentecostal and tongue-talker, but God told me it wasn't of Him. So I've had a vested interest in finding out what exactly modern tongues is. The fact that so many people are deceived by it doesn't mean they are possessed by an evil spirit. In my studies I've discovered that modern tongues is a mere human ability, and anyone can do it if they try hard enough (it takes "letting go" of control of speech, which is very difficult for most people). I certainly understand why many think it is devil possession.
So true tongues described in the New Testament is actual languages that can be understood as in Acts 2. That is miraculous, whereas modern tongues is not. Just because someone can speak nonsense fluently and make it sound like a language doesn't mean it's the same thing as Biblical tongues. I recommend this book, if you can still get it:
https://www.amazon.com/Tongues-men-...003&sr=1-2&keywords=tongues+of+men+and+angels
However, it's very expensive now because of its rarity. I bought it years ago and only paid $11.
Also, this video is a very good analysis:
May God bless you and keep leading you in His ways.