Swaziland national team

Appointed Swaziland head coach in 2012 on a one-year contract,^[5] Billen was bought a new car by the National Football Association of Swaziland as a mode of conveyance was one of the rules his contract embodied.^[6] With a monthly salary of 100000 Swaziland lilangenis,^[7][8] and the Swaziland Football Association spending 40000 on his rent, the Belgian's first match was a friendly against Lesotho in October,^[9] losing 2–1.^[10] Two days later, he helped them achieve a 1–0 victory over Lesotho again.^[11] Praising his players for their efforts that game,^[12] his charges held Lesotho to a 0–0 stalemate^[13] in their third and final friendly in preparation for the 2014 African Nations Championship qualifying two-legged round opposing Angola,^[14] losing 1–0 both legs. That same month, the former footballer stated that his desire was to work with local coaches and predicted a rise in the FIFA World Rankings, claiming that they would improve dramatically over time.^[15] In 2013, he went with the national selection to participate in the 2013 COSAFA Cup, not having a presentiment of failure and predicting that they would overcome all seemingly insuperable obstacles and deliver a good showing in the tournament;^[16] however, despite a draw with Botswana in their opener,^[17] the Sihlangu never progressed past the group stage, losing 2–0 twice to Kenya and Lesotho with Billen reconsidering his job as coach.^[18] Being thrashed 10–0 by Egypt in a friendly worsened the trainer's position, with fans requesting for his immediate dismissal as they were not expecting such a scoreline;^[19] but, despite fan pressure, the National Football Association of Swaziland still did not sack Billen^[20] until November 2013, with local Harris Bulunga taking up the interim post.^[21] The reason they gave for his firing was that he was in Belgium too often and spent more time there rather than helping the Swaziland Football Association.^[21]

The coach temporarily returned to Belgium to care for his mother, who was ill.^[22]

One year succeeding his appointment, Billen criticized his Swazi coaching colleagues, saying that they never allowed him to share his ideas.^[23]