Ipad mini 4 connect only to 3G not 4G

I had bought a iPad wifi + cellular went down to Verzion to activate it, they gave me a sim card and it would only get 3g so they switched out the sim with another and the same thing happened, they gave me an excuse talking about it must be the ipad. So I switched the sim with cell phone sim card which looks different and voila I got 4g, so I went back to Verizon and told them that the sim card isn't right, they switched it out again and nothing but 3g sp I went to best buy to see what sim cards they had, they had the black card sim and the white card sim, i told them that Verizon used the black card sim so they used the white card sim and they switched it over and LTE came up on the ipad