I had the same problem, you literally just need to unscrew your controller and clean it a little.
Trust me, its really simple to do and will go back together just fine. I know its a little scary opening something you paid £35 for but its not going to break unless you start attacking it or have extremely greasy hands or something.
You'll need a Torx 8 security bit screwdriver to open it, however I managed to open it with just a regular Torx 8 by snapping the security piece.
The hidden screw is under the barcode in the battery compartment.
Good luck