Can’t call 0860 numbers

I recently started have problems when trying to call certain business call Centre (0860 numbers). When I visited the Cell C store they advised that you can’t use the airtime that included in your contract to call these number, yet I have proof that I have called 0860 number before and never had an issue? They confused that their system has allowed me to call 0860 number but can’t tell me why all of a sudden it changed. cell C is the only cell phone company that does this. Other cell phone companies just charge a higher rate to call 0860 number. Most big companies such as the banks use 0860 number When their customers need to contact the call Centre. This. Restriction limit cell c customers.