This falls into an area where it is easy to do damage. I am not sure of the current price/value of the 1100D but consider whether it is worthwhile to send it to Canon to get it properly serviced. A large camera shop MAY have a competent individual that can take care of this without damage.
It has been a LONG time since I have dealt with cleaning high quality optical surfaces with anything other than the usual cleaner but near pure methanol used to be the cleaner of choice since it is reasonably aggressive and doesn't contain any contaminants that will be left when it evaporates. Check whether any of the cleaning fluids are composed of this or a modern alternative that is sensor friendly.
If you have a stain then you need something sufficiently strong to attack it after which you will need to effectively flush that area once the cleaner breaks it up so you will probably need to use multiple applications of cleaner and swabs. Resist any urge to put pressure on the swab or you are likely to cause surface damage to the sensor (or the anti-aliasing lowpass filter that sits on it). If a proper cleaner for the stain is available it will break it up without pressure and then it is simply a matter or removing the residue while it is still in a liquid state via multiple swabs and perhaps a second treatment. It is likely the original spots, once dried, are resistant to the typical cleaners aimed primarily at providing a liquid attractant causing dust and small particles to stick to the swab.
Rodger
EOS 1DX M3, 1DX M2, 1DX, 5DS R, M6 Mark II, 1D M2, EOS 650 (film), many lenses, XF400 video
