Diference b/w wip_close,wip_abort & wip_shutdown

I am confused with the actual process that hapens when wip_close,wip_abort & wip_shutdownAPIs are called.
The scenario is like this, I am uploading the file to FTP server at this time the GSM data call comes,to receive the cal i will have to stop the FTP process. For this am using wip_close(transferchannel) & then wipclose(FTPchannel).this works fine. but after the data cal if i try to write the file in FTP(file with same name which was stopped in betwen) I am getting the eror 550 in TRACE saying that this file is being used by others.and also I cant delete that file from FTP server it reapears every time I delete it.but when i make data call once again and disconnect,the FTP process goes smooth again writing to the same file.
I am really confused now what to do .Please tell me wat exactly I ve to do using any of the above mentioned APIs