It stays unclear what "stops" in your case.

For resuming an interrupted download, use the "i" option (see the manual). It
worked fine for me so far.

As for the "PAYING": you certainly did not pay money to the original creators
of this free software. But you may have given money to some other parties. See
also this FAQ:
 <https://www.httrack.com/html/faq.html#QG0c>
So, in case you paid for it and have an SLA with the "other company" who sold
you this free software product, you better contact them for any kind of
support.