Help with tax on advertising services

[alisidd]

i run a freelance graphic designing setup.Designing of packages,cover designs,brochures,skillets,hoardings,banners and cartons are my major provisions,my customers are well known registered companies who have been deducting income tax @ 6% on my bills, recently I've been informed that from now on my bills will be entitled to 16% WHT which will be in addition to income tax already been deducted.I am not registered for sales tax and my basic concern is, giving the nature of services i render am i entitled for such tax and should i register for sales tax???
I need serious help with this...please reply ASAP