Beware of BT games vouchers

My son wanted vbuxs and we were told by Kyle at canal walk branch that it is safer to buy a voucher from them instead of logging in our banking details. We then purchases the R150 voucher with our 10year old savings. Spend the rest of the day at canal walk and when we got home and tried to punch in the voucher on the ps4 it said that the voucher has already been used. The Sunday we drove all the way back to canal walk to tell them about the problem and then Kyle said he would have to email head office about it and will get back to us. At 1 Sunday they sent us an email to say we used the voucher. Trying to make it seem as if we were trying something *****. As if it didn't just cost us R150 petrol to drive back. And our son can't access anything on the ps4 without our permission because of parental control. Please beware of bt games because now we left with a disappointed 10year old with no money and no vbuxs.