Hate to say this, but I used to see this from time to time with different phones when I was a tech at Sprint. It was usually 1 of 2 causes; either liquid damage or physical damage to the charging port.
You might have a prong in the port that is loose, bent or even broken. Most of the time though, it was liquid damage. Do you see any white or green in the charging port? Might even be just a slight amount in the back of the port, it can be hard to see. If neither of these are the case, you might just have some gunk in the port that is making the phone think it is still plugged into a charger.
Maybe try blowing out the port with some canned air. Just make sure that you don't point the can down, then you're going to blow that crap from the can into the port. Or you could do what I used to and clean the port. You'd need an small toothbrush, like a child's toothbrush, and something like alcohol. If you can try something more pure than the 70% rubbing alcohol that you get in the health section of a store. We used to have something that I think was 97% or 99% alcohol for our repairs.
If you do this, be sure to dip the toothbrush in the alcohol, then shake it once or twice to get the excess liquid off the brush. Then just kinda dig in and clean that out. I usually brushed for just a few seconds. After that blow into the port to dry it out. Hopefully that fixes it if you need to do this. If you're not comfortable with cleaning out the port, don't do it. It's not worth breaking or ruining the port for an annoyance.
That sounds like alot of work, and I think it might be for a phone as old as the Surround. If you can, you might see if there is a Sprint repair store in your area and just ask if they'd be willing to just clean out that port. If you're lucky, they'll be cool and help you out, just be nice to them. I used to help people like this all the time if they were cool to me. Just remember that this is also just a temporary fix if there is some liquid damage in the port. You can clean it out, but it WILL come back.
If it's neither of these things, then I'm sorry for the wall of text and hope your phone starts working right. Sometimes they just go crazy for a while for no reason at all.