Can anyone help with this one please

I bought my house in 1994 at the it was work £26000 I was put in band Bbut after doing a check I should have been in band A because it was under £4000 , now the thing is the year after I bought it I had my loft turned into a bedroom without any extensions and it was then classed as 4 bedrooms instead of 3bedrooms , I an now wondering if I try to change my council band to A and claim back money cos I was in the wrong band that I might be put in a higher band because of the improvement I made I E the loft bedroom , my naighbours are in the same band and one of the As added an extension the other one as done nothing to her house , so now I’m worried if I try to change the band I will make it more expensive, thanks for reading