According to the specs on your bike, it's supposed to have a Bicycle Only mode, which I assume means you just pedal it. These bikes seldom have instructions, so you might want to fool around w/ all the settings and see if it has that. There also may be a way to take the plastic box off the controller and unplug the speed limiter and get 20MPH. I did that on my Ancheer, which is sorta like yours ($600 bike). Can't remember what color wire it is, it's often a jumper wire.
If you get tired of the bike, I highly recommend the Ancheer below. I'm on my 2nd one, just wore out the last one on a long commute 7 days a week for 2 years. The best part about the bike is that in addition to two pedal assist modes it has a throttle as well, and w/ that you can choose to not use the battery and pedal it like a regular bike. These are extremely dependable bikes.
Thank you for the suggestion. It goes 20, and has a thumb throttle. I got all the settings for the S866 and made sure to check all the settings. I set the speed to 100, disabled cruise control (5 seconds on the throttle turns it on), and set pedal assist to be off at the lowest setting. Unfortunately, cruise and pedal assist didn't change. If I turn the bike off, it is all pedal, but that's just my work-around for now. It may be a setting I've not found or be at the controller. I'm sure there is a way to turn it off with the power being on. Really only bugs me at night though, since the power has to be on in order for the headlight to work. My wife's bike is the same way, but both were listed as having 3 modes (pedal, pedal assist and throttle). The listing was for the UPGRADED MX300 (we received the MX350), so I am assuming that they just didn't set something correctly, since it is the new version.
I looked at the Ancheer and had that in my top searches for a bit. Looks like a great bike. I went with the Cliensy (Eshylala I think is the OEM) because it was folding, 350W and had good reviews. I also found a vendor on eBay that would negotiate. I think the features of the Cliensy and Ancheer are pretty close.
Folding is important to me. I can fold both bikes and toss them in the bed of my truck (Tacoma) with the tonneau cover closed, and still fit some luggage. This way if it is raining, the bikes don't get wet. Plus, my tail gate locks so no worries if we stop on the way to our destination.
Now I need to lock the battery to the bike, so I can stop and get a meal or shop while riding. I've got a U style lock for the bike, from my older bike. May see if I can find a bigger one that will go through both tires when folded to lock it that way. I had a friend suggest a chain lock for the battery bag. I found one with a built in alarm. May give it a try.
I really love this bike. It rides nicely, shifts gears smoothly and is easy to pedal. Small squeak in the front tire at first, but it was just an adjustment. I'll probably upgrade to a bigger battery/higher wattage model in a year though and give this one to my daughter. The assist bugs me, but is more an annoyance. I am sure I'll figure it out. I'm going to research the controller next and see if there is a dip switch or something there to correct it.