I am so sorry Neets that you've had this 'protuberance' following your surgery.
I had a lumpectomy near my nipple & existing fat in the breast (which was larger than the other breast), was 'relocated' to fill in the 'gap' ... but over the last 7 years, it has 'subsided' into a bit of a 'dip' rather than becoming a lump. My surgeon had offered to 'fix it' - but I've chosen not to.
But your issue, really needs major discussion with your surgeon. My own opinion would be that they should 'fix it' at no charge to you.
Do you have a Breast Care Nurse? I would contact them & see if they can 'intercede' on your behalf, to arrange a meeting & discussion re rectifying this unwanted development.
It should not have happened.
Take care .... and all the best for a good resolution xx