When I typed in Quixbelt, Google thought that I meant Quixberg or Quixberger. Even though it vaguely recognises those surnames, there are no results for any of them! They're certainly German.
I wonder of they are related (distantly) to
Quixote,
Quixada, or Quoxano. Its not likely...
I'll tell you what, Quixbelt might be a variant of a more common surname. If the original form was spelled with a K, then it might've been converted to a Q..?
I know practically nothing about German or Dutch etymology, but I hope that you eventually find answers from someone who's smarter than me!
https://www.behindthename.com/polls/356294https://www.behindthename.com/polls/356351https://www.behindthename.com/polls/member/181370