Hallo:

[Is there a way that I can resume but using another file and server?]
Yes, with some servents, eg. Gnucleus, but only if the two files are identical down to byte level. With different files, no. Imagine the difficulties to make sure the file parts will fit together...

[Why is it that when I abort and resume one file, it keeps trying to start from the beginning, but when I stop, it tells me the farthest I have gone in the download?]

With my servent no problem (Gnucleus), if you tell us which one you are using we will surely help you further. As said before, the more information you give, the better will be the answers.

Greetings....