Caltex Gift Card not working

Won a R250 Caltex Gift Card in a competition sometime ago. Valid till 9/21. If I want to use it it says no funds available. Wrote an mail to the lady that send it to me to check my balance. Only R169 left of my R250, Caltex takes fees because I do not use it?? Try to put in R160 still not working....**** or what?