Vodafone — Network suspended

My mobile number is [protected]. This number is more than 15years old recently sim changed from 2G to 4G and also plan has been changed from prepaid to postpaid. But from yesterday my network connection suspended the reason of which is still not known to me. Your Uttarpara service center told me that as I requested for prepaid plan for that the network connection suspended. I don't understand how my network connection suspended without my permission when this number is absolutely necessary in my day to day life particularly network banking etc. So please look into the matter and arrange for network connection immediately otherwise I shall have no option but to change service provider.