Make 2 columns NOT going to 1 column for smaller devices

[cathy007]

I am having trouble making 2 columns got to 1 column for smaller devices. Although I have set up a 2 column row using the 2 column brick - column width left at infinity, when it rescales it is still 2 columns for the smaller devices, How do I set this to 1 column for different break points? Probably some easy thing I am missing.

I am pretty sure it worked automatically before but now wont adjust. any help would be great ciao Cathy

[SENEK]

if 2 column:
width of 6 on each column for a total of 12 and it works
if you put infinity it will reduce all the column to fit on the width

I put a heading content on each column but just to put something inside