This happens on a lot of makes of cars, it happened on my previous Vauxhall Tigra Convertible. The fault can happen irrespective of year of car, as it just takes a resistor to blow, and your knackered.
To get a 4 speed cabin fan the cheapest design solution is a 'plug-in Resistor bank' that will change the voltage from 12V full speed, down to 9V, 6V, then 3V slowest speed, using you fan speed position switch.
When the resistor bank burns out it is almost certain to just leave the 12V speed only, so you only have the high speed fan position working (position 4). You do need to sort it out, as if you run on high speed continually, you will likely blow the fan motor as well, as they are never intended to run on high speed all the time.
The plug-in resistor bank on a car is cheap, usually under £20, and its just plug in obviously as the name implies.
The harder problem is to locate it and it is normally in the air flow of the air duct before the fan, so it can be cooled as it heats up being resistors.
You will have to buy the correct resistor bank for your Ecosport, year and whether pre-facelift model or facelift model. Good luck.
I was interested in the question about the heater fan only working on full speed. The old Rover 45's used to suffer with the problem and the fix was fairly simple. The Rover Resistor was a bit cruder than the one ColinJYD suggests but it was a case of removing the glove box and the resistor was behind it.
I tried to look up about Ecosport heater fan resistor and could find little except offers to sell one. The nearest I could find on how to replace it was on a Fiesta. In that case it seemed to be a case of carefully removing the cover beside the central hump in the footwell. Of course it was LH drive but it appeared that the resistor was mounted behind the heater speed control on the side of the heater housing. Two screws held it in place. Presumably it will still on the same side behind the heating controls . I find it lamentable that there is so little information. IN days of your, even without Haynes one could find all sorts of helpful tips on line. If Colin cant find a how to do it then there won't be one
The way I found the resistor pack on our Vauxhall Tigra convertible was to trace the wiring (colour coded) from the fan motor back along the cable loom to the resistor pack. Its a difficult method, but I found it eventually.
As said, depending on car make and model, sometimes the resistor pack can be found easily behind glove box plugged into the air vent, or it could even be under the bonnet at the very back next to the bulkhead, requiring removal of the windscreen wipers plastic scuttle or other such removable plastic panels, to get to the incoming air supply of the air vent where it could be located close to the intake. (your looking for electrical wires/socket going into the air vent).
In other words it could be located anywhere, all the way from the air intake right down the vent shaft to before the cabin heater matrix, as it must be cooled in the air vent.
One other suggestion is go to the Vauxhall parts department and ask them to pin point the location of the plug-in resistor pack on their parts screen. I tried that with our Tigra, and the printout they gave me was rubbish as it was for a Corsa DOH, they had no idea