In Belgium, minimum rates of pay are not regulated by law but in collective labour agreements which have a general binding effect.
The Collective Labour Agreement for Road Transport and Logistics on Behalf of Third Parties, specifically for the subsector of mobile workers, makes a distinction according to the payload of the vehicle and the seniority of the driver in the sector. Depending on the currently applicable regime (August 2019), the rates range from € 10,7295 to € 12,1040 gross per hour. For more details on the salary scales you can consult the agreement (available in English under the name: JC 140.03 Road transport and logistics on behalf of third parties: mobile workers) here. A useful overview of the remuneration scales can be also found (in Dutch only) here.
If you want to obtain more information about your wage entitlements, you can get in touch with the trade union here.