There are two ways to get a Congressman to respond to a citizen’s concerns:
1) Have a big fat donation check in your letter
2) Primary him (he’ll respond during his desperation period when he realizes he may lose)
My attempts at writing senators /congressmen started with the run-up to the GCA of 1968 when I was stationed in Germany. The Act passed and cost me a cherry Browning Hi Power and Walther PPK. Then and for many ensuing decades I found that writing about my issue (gun control) was an absolute waste of time. These useless democrat (and occasional republicans) bastards are beyond reach since their loyalty is strictly to the party line and not the USA. I gave up long ago.