Both seat belts stopped working. Could this be a fuse?

The physical function of seat belts coiling and uncoiling is entirely unrelated to any electrical function. Therefore, there are no fuses involved in that system -- for pulling them out, latching, unlatching, and having them coil back into their retractor assemblies. If the belts stop short, they could be twisted, the retractors could have internal problems, they could be dirty, or for the passenger seat, the child safety seat retractor lock may be engaging.