Hi Teresa,
I think thereis a misunderstanding in the way you try to solve your issue.
The transaction you mentionned : ZSD_CUSTOMERS & ZSD_CUSTOMER_MASTER are specifics, which means they are related to something that has been adapted to your system / client from the SAP standard.
The double line issue is probably due to a bug in the code. If you want to extract your data without using a specific implementation (i.e Transaction in your case), you can learn how to make some "Queries" from SAP through various table, or directly ask the table that record all the data for your Customer.
But for the beginning, you need to learn how to use the SE16N transaction properly in your system. Then, in a second time, read the table named KNA1. Like this, you'll be able to reproduce what your specific transaction is doing without the buggy thing.
Have a nice day,
Please reward if Help.
Emeric.