This is from a Canadian point of view, but the rules regarding how corporations run is generally pretty standard. I took a few classes in corporate governance, but I'm working mostly from memory, so hopefully most of the information is accurate!
A corporation is its own entity, separate from any shareholders, and it can make whatever policies it wants. Unless you are an officer or on the board of directors, your participation in the company usually will be limited to voting in shareholders' meetings and receiving dividends. Refusal of service is a policy matter, so the fact that you are a shareholder (or anyone else, for that matter!) should be irrelevant. In fact, you might be denied service because you're an officer due to conflicts of interest.
If the company was unincorporated, you may have more rights, but you'd probably be subject to some sort of agreement.