I‘ve been through this several times. While writing my thesis I drank 20-25 cups of instant coffee per day. After that, my highest consumption was around 7-8 strong cups. I went cold turkey several times, it works (2 weeks with headaches and fatigue usually), usually for months until I slowly start drinking 1-2 cups again. Also tried:

* more complicated coffee preparation, i.e. ditching the automatic coffee maker for an Italian machine with long warming-up times and manual bean grinding. Doesn‘t really work, I just made stronger, larger cups

* coffee that doesn‘t taste good - without sugar, mediocre brands, capsule machine - works somewhat to reduce consumption but requires discipline

* no coffee machine at home or at work - works well, though takeaway coffee can be very large/strong (300+ mg caffeine)

* caffeine pills - worked because the habit/taste is not a factor, so dosage was under control

What I haven’t tried but might work:

* have fixed times for coffee (e.g. 3 times a day, 8:00 11:00 15:00), if you’re the type of person with a very structured day

* decaf every other cup or similar

Good luck!