Paid for minutes and data removed from my number with zero communication

After a 24 month contract plus a few months of month to month, I requested that my number be converted to prepaid.

I purchased 3 gbs of data 2 weeks ago, of which I had about 800mb left plus over 200mins. It's the morning of the 31st August and all my data and minutes has been wiped clean.

A) I was not advised that this would be removed if I converted to prepaid. The data I purchased clearly indicated that it was valid for 30 days

B) Please refund me the data and minutes that I have already PAID for