End of My prepaid o2 is tomorrow. I ordered a postpaid from Mediamarket so it has a new sim card and asked them to keep my prepaid SIM card because  l want to use my prepaid number postpaid. They told me it takes time around one week  .But today I got a Sms which mentioned to automatically charge my prepaid. I don't want it recharge . I am afraid the o2 has my bank account info . I only want to use postpaid. How can cancel automatic prepaid ?