Employees taking cash money

I was charged R400 for wheel alignment that wasn't done and charged R600 the next day to do wheel alignment. The employees claimed I wouldn't get an invoice if I payed cash and I would be charged less for the services but i still feel cheated. What kind of wheel alignment is R1000? And why no invoices given. This happen at wonderpark tiger wheel and now that I think about it, its not possible that a big company like this doesn't give a slip or invoice and they require cash.