The "control box" you mention is actually the battery meter box Jill, the controler box is at the rear of the battery mount. The throttle only (I pressed in) or pedelec (O pressed in) switch is mounted in that meter box of course.
It sound to me that you mean it's on pedelec all the time, power only when you pedal and the throttle increasing it's rate.
If so, that means the rocker switch isn't connecting when it's operated into throttle only mode. The cause will be one of the following:
1) A faulty switch.
2) One of the two wires to it broken.
3) A poor or corroded connection in the five way socket under the battery platform.
4) A controller fault.
The most likely is number 3 since this area is vulnerable to damp, if so it shouldn't be costly to fix. To do that, you should take out the battery and then turn the bike over. Underneath the battery platform you'll see a tangle of cables, cut any strapping that's prevents you from getting to them , then unearth the bundle of cables. There will be two swollen points in the sleeving which are the two connectors, and it's the larger one you need to get to. Cut away the insulation to reveal the flat black connector within, then press the release catch on its side and unplug it. Then plug it in and out a number of times to clean and remake the connections.
Now right the bike without insulating or stowing the cables, replace the battery, switch on and see if the switch operates between the pedal applying power or only the throttle doing that.
If all's well, upturn the bike, reinsulate the connector thoroughly with PVC insulating tape (from a DIY store), stow the bundle of cables and tie them in place so that they cannot foul the rotating cranks or chainwheel.
If that connector isn't the answer, it will be one of the other causes, needing some skilled attention, but lets cross that bridge only when necessary.
.