On your billing question... no, there are no additional charges that I'm aware of. If you got a phone call request, that's automated by the site and didn't come from me.
Thanks for the additional info on the treadmill. I've been working on these things for years, and the symptoms you're describing are almost always indicative of a worn walking belt or a worn walking deck. One (or both) are the cause of these symptoms in the overwhelming majority of cases (probably 75% or more).
In rarer cases, this can be caused by an aging motor or even a belt that is too tight. The motor isn't worth discussing, in my opinion, as the rarity just doesn't make it reasonable. And if the symptoms started before you were playing with the tensioner, then the tightness isn't the problem either. So I would focus on the worn walking deck or worn belt.
If this is something you want to troubleshoot and repair yourself, let me know. The procedure would include using a multimeter to measure the current output of the motor under various loads (slow, fast, incline, etc.). There isn't really a visual test we can do (not reliable enough). If you're doing the work yourself, the belt is usually cost effective to replace. It's $100 for your model and can be purchased >>here<<. The deck is usually cost prohibitive ($200). It can be purchased >>here<<.
If you'd rather not dig into the treadmill yourself but still want to have it repaired, just let me know your zip code and I'll see if there's a certified servicer around you. It'll cost $50 or so to have the treadmill evaluated.
I hope I've answered your question. If I can do anything else, just ask. Also, please remember to rate the service you've received. That's the only way the experts here are credited for assisting. I hope your experience was great!