T-Moblie Get less than you paid for , Internet

T-mobile prepaid broadband service:  I have been buying prepaid cards which provided 1.5 GIG of data.  New cards do not have the same information printed as did the old cards. I found out why.  When you call in the automated answering systems tells you you don't need to talk to anyone, just scratch off the strip in back and read the number. I did this.   Three days later my service "ran out".  When I called to complain, they told me I didn't choose a service and since I didn't choose a service I was enrolled in the $0.20 a megabite category.  Question: If "you don't need to talk to anyone" how would you enroll in any service?  Why would anyone choose less than 100 meg over 1.5 GIG?  I wonder how many others they stick like this.  Kind of a bait and switch I think.