Problems with a 150mm 2.8 APO MACRO EX DG OS HSM

I have a 150mm 2.8 APO MACRO EX DG OS HSM repaired under Warrantee for, jarring image as OS engages, a lot of noise, as if lose bits in the lens and underexposing, in macro 3-4 stops in June 2016.
(The under exposure is not present when using a Canon 2.8 100mmm macro lens)
On the return on the lens in 2016 the problems remained uunfortunately we needed to move house and all my energy was diverted into this. The lens was packed, along with most things, away while this was done. Earlier this Spring I unpacked the lens to try it again and found it unusable due to, as before, image juddering, noise and in macro grossly underexposing.
I return the lens for assessment and this I did only to be told there would be a charge of nearly £110, since reduced to £83. I realize I am out of warrantee but that due to moving I was not in a position to deal with the poor repair originally done, one that appeared to have had no effect on how the lens performed at all.
They are saying they will replace the image stabiliser (which is clearly defective), but I have some concerns, not least I still feel as not repaired properly the first time that I shouldnt be paying at all.
How could the stabilizer be causing the under exposure (present with or without stabilizer in use) which make the lenses near unusable in macro?
As important, or maybe more so, if the repair failed last time as soon as I used the lens (this is the only lens I faithfully turned off the stabilizer before then turning the camera off before removing the lens. I did this as I had read warnings on Sigma and taking there lenses off with the stabilizer still engaged. I use Canon, Sony and Tamron lenses, all stabilized and non-have ever had a issue or needed repair, just the carefully handled Sigma one).
Feedback on these issues would be very welcome.
(The under exposure is not present when using a Canon 2.8 100mmm macro lens)
On the return on the lens in 2016 the problems remained uunfortunately we needed to move house and all my energy was diverted into this. The lens was packed, along with most things, away while this was done. Earlier this Spring I unpacked the lens to try it again and found it unusable due to, as before, image juddering, noise and in macro grossly underexposing.
I return the lens for assessment and this I did only to be told there would be a charge of nearly £110, since reduced to £83. I realize I am out of warrantee but that due to moving I was not in a position to deal with the poor repair originally done, one that appeared to have had no effect on how the lens performed at all.
They are saying they will replace the image stabiliser (which is clearly defective), but I have some concerns, not least I still feel as not repaired properly the first time that I shouldnt be paying at all.
How could the stabilizer be causing the under exposure (present with or without stabilizer in use) which make the lenses near unusable in macro?
As important, or maybe more so, if the repair failed last time as soon as I used the lens (this is the only lens I faithfully turned off the stabilizer before then turning the camera off before removing the lens. I did this as I had read warnings on Sigma and taking there lenses off with the stabilizer still engaged. I use Canon, Sony and Tamron lenses, all stabilized and non-have ever had a issue or needed repair, just the carefully handled Sigma one).
Feedback on these issues would be very welcome.