My advice on this would be to just ensure that you can feel your biceps and triceps working hard on each rep of each set. Concentrate on feeling and making the muscles do the work. I would stick to the movements that allow you to handle the most weight (
standing barbell curls, db curls, cable curls, etc for biceps, and lying
triceps extensions, cable pushdowns, dips, etc for the triceps). Then, make sure your post-workout nutrition is A-1, and the 3 hours following each workout. If this is less than optimal in nutrient timing and intake, then you will get less than optimal results.
I would also try lowering your overall volume for your arms....instead of the volume you listed, try only doing 5-6 sets total for biceps and same for triceps. Focus on hitting them with slightly heavier weight but for less overall sets, and see if this helps some after 3 weeks time. Make sure tho that you don't go too heavy with the weight, and make it so your intended muscle group is not doing most if not all the work. Find that perfect balance, of not too heavy, but not too light. This unfortunately can take some trial and error, but it has to be done.
Of course, you have to make sure everything else is in order as well...like your daily nutrition, water intake, sleep, etc...so look at all aspects and aim to improve on everything.

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Sit back and ask yourself.....why aren't my arms growing like they should be? And then go thru a check list of possible things. Such as....
1) Am I hitting them hard enough? Too hard?
2) Am I taking in enough overall calories to promote growth?
3) Am I taking in enough of the RIGHT TYPES of calories at the right times to initiate growth?
4) Am I taking in enough protein every 2-3 hours of each and every day?
5) Am I getting adequate sleep so that I can properly recover and grow from my workouts?
6) Am I taking in enough water (1 gallon per day on average)?
7) Is my post-workout meal (and the meals within the 3 hours after training) the right types of nutrients to be taking in during that time?
8) Am I supplementing optimally to get the most results possible?
9) Am I doing extra activities other than my training which could possibly be using up the calories I take in that are otherwise needed to build new muscle?
10) Am I over-stressed from daily life?
11) Am I overtrained?
12) Is my motivation as high as it should be?
13) Do I, or have I missed meals on occasion or frequently?
14) Am I making a continual effort to do more each week that I work my arms. (as in, either get more reps, or lift slightly more weight)? In other words are you forcing your muscles to adapt from week to week, and actually giving them a reason to grow?
These are just some of the things you can ask yourself honestly to find out if you are on track for putting and keeping your body in an anabolic state. Be brutally honest with yourself with the above questions, and then do whatever it takes to rectify the things that may not be up to par.