I had to give this one some thought. At first, I was not sure this question belonged on this blog because it is not about a fetish. However, as I pondered the issue, I realized that the solution is all about a fetish.
I have done extended edging, an intense form of tease and delay, with many people and their balls never increased in size. They will get tighter, making them look ever smaller. I know you do not want that outcome, so this must be ruled out.
As you discovered, chastity will not increase the size of your testicles. It will likely give a person blue balls, but in your case, they would be tiny blue balls.
Even long-term chastity is not going to solve your dilemma.
As a Mistress who is very fond of CBT (Cock and Ball Torture), I can tell you that testicles will get rather swollen after being repeatedly kicked, kneed a few times, stepped on, or struck with something like a riding crop over and over.
You need to be realistic in your expectations. Your balls will get about half again larger than they are now, but they will not reach a reasonable size. The effect is not permanent either, so this is a temporary solution at best.
With severe ball torture, you may achieve the larger balls you seek, but they can be permanently damaged which is why I avoid going to that extreme.
Since I am a phone Mistress and not a physician, this is out of my area of expertise. I did search online and found several websites that talk about regular massage of testicles being very useful in increasing their size.
I cannot link to outside websites here, so please do a web search for “how to increase the size of testicles.” I found a wealth of information and so will you.
In the meantime, you may have fun exploring some of the temporary fixes achieved by ball torture.
Best of luck to you, shrimp balls!