Hard to say what actually worked for me but I got an SAR after getting my citizenship approved after waiting 18months
I followed some of the suggestions here and when the complaints team fobbed me off, I repeated my request to delete all other names apart from the one I used my passports, as SAR showed some duplicate entries for some reason
However, after 12 months they asked me to give them my address history again inc. the actual day of the months which wasn't part of the application form, and seemingly it got approved after 6 months but it took another email from my MP to get them to read my reply after like, a few weeks