Shall I be listed as technical program committee member if I accepted an invitation and did three reviews? I receive often invitations to serve as TPC (Technical Program Committee) member. Some are from my colleagues but some are just from random people who I don't know. 
If I agree to serve as TPC member then I get papers to review and this is the only task assigned to me. 


Shall I be listed in on the conference TPC member list in this situation? 
Is it ok, to ask the organizers to update the webpage?


In fact, I am only a reviewer, but I invest my time to read the papers and write the feedback. I treat it seriously and reviewing ~10 pages paper may take me up to 3-4 hours. It is pity that I don't get any mention on the official webpage although I have contributed my time and expertise.

Comment to the accepted answer (I don't have commenting privilege yet): I accept the interpretation A of your answer,  because the only duty of a TCP member for the conference that I got in my mind is to review (or delagte the reviews) for several papers.
I am not sure if I understand you correctly. Basically, there are two ways to interpret your question:


Interpretation a) you have been invited as a member of the programme committee, did the duties associated to the role in this conference (for instance, but not necessarily restricted to, reviewing papers). In this case the answer is unsurprisingly that yes, you should be listed as a member of the programme committee. It is completely acceptable to remind the organizers to add you to the website if your name is not listed if other PC members are (it is conceivable although unusual that a conference would just not list the PC on the website).
Interpretation b) you have specifically not been invited as a PC member, but as a reviewer (or in whatever other role), but you feel that you did the same work as a PC member. In this case, I am sorry to say that there is no obligation for the conference to somehow upgrade your status, and mailing them about it is unlikely to lead to anything else than you seeming somewhat needy. It is not uncommon or immoral for conferences to distinguish between different roles (e.g., reviewers without voting powers and PC members with voting rights in the PC meeting), even if most of the "work" (writing reviews to papers) is the same or similar. That reviewers don't get mentioned in your case is certainly unfortunate, and you have every right to just not agree to be a reviewer anymore for this conference, but it's not inherently immoral or oblige the organisers to upgrade your role to a more visible one. The underlying faulty assumption here (which I assume is an easy to make mistake given how many conferences at least in CS nowadays work), is that reviewing and being in the TPC is the same. While is is indeed true for many conferences, there are plenty of exceptions as well. In many, particularly very strong, conferences, there are multiple layers of reviewers, PC members, senior PC members, track chairs, and program chairs, with increasing impact on the actual selection.