I have some information on the sister whom i would like to see
If I were you I would not count on a possibility that her sister Maria speaks English. Maybe her children or grandchildren do, if she has some. But why don't you try a regular mail for the first contact? Air mail should take less than a week to go there (I assume you are in US). You can write it in Polish or English or both and I am sure someone could help you to write it in Polish. But even if you write it in English they should be able to find somebody in this town of population 40,000 who could translate it to them. In the letter you could set up other contacts possible. You did not say how old she was; she might be dead by now, she might be very frail, etc. Or she might be all dandy, you never know.
Problem is, your mail address is incomplete and only partially correct. You missed the street and appartment number, and the street name was wrong. The corrected address follows
ul. Śniadeckiego street-number-here
In my previous post I was assuming that you in fact have the complete street and apartment number to Maria Cudak, but you just did not post it here for whatever reason. I also knew that the street name you posted was wrong because "ul. Snioleckiego" street does not exist in that town. But "ul. Śniadeckiego" (Śniadecki's Street, with S acute) do exists there - and this is the closest matching name - in downtown Oświęcim. The postal code was correct - as this is the same code for the entire town. [It seems useless but even in this fragmentary form this simplifies the letter addressing, since you do not need to specify a county and a voivodship.]
But just in case you in fact lost the street and apartment numbers to Maria Cudak you can retrieve this information by contacting an appropriate office in Oświęcim Town Hall. The procedure is like this:
+ You fill an application form requesting specific data about Maria Cudak and providing your own contact data and optionally data of your proxy person in Poland. There is a space where you suppose to justify your request. The sample of the form to fill is here in Polish
+ You (or rather your proxy) pay 17 złoty for the certificate or just a written statement from the office and 31 zloty for the access to individual data.
+ If Maria Cudak is alive and willing to provide you with her full adress then you will get the certificate with her address. Otherwise the office will notify you about her refusal, etc.
They are required by law to provide you with the answer within one month from the day of your application.
This procedure is part of the national program for protection of private information. It is described in Polish on this page
At the top there are names and phone numbers of persons competent for providing you with such information and dealing with such cases.
The name of the office is: Wydział Spraw Obywatelskich (SO) [Department of Civil Affairs] .
Here is a page with all officials from this department, including their email addresses. This gives you an opportunity to write an email directly to the Head of the department (Fijałkowska), or to any of the four ladies mentioned on the other page and qualified for providing you with any related information: Beata Franiczek, Agata Klęczar, Anna Latko, Bogusława Wądrzyk. Claiming ignorance you might be able to cut the red tape a bit and speed up the process. They are not required to provide you with Maria Cudak's phone number, but - who knows - they might just do you such a favour.