Hi there!
Sorry to hear you had such bad service and I'm glad it's now all been sorted out fully. I'll just give you a brief explanation of what I think happened there.
In terms of the direct debit, I'm not sure why you weren't informed. In most cases NTL sends out an initial letter, reminder notice and final reminder if payments are not being made on the account.
In terms of being downgrades, downgrade orders are automatically generated and until a restore order has been put through, you will have no service. It changes from billing system to billing system, but generally restore orders take around 24 hours to go through, similarly it takes around 24 hours - 96 hours for payment to register on the account.
Accounts get scanned on a regular basis and those found with high outstanding balances, or a single penny over the Credit Limit if you are a credit limit customer, will get automatically downgrades. (If it takes up to 96 hours for payment to clear on the account, there is still a chance the account can be downgraded again even after payment has bee made).
I'm glad that the service has been sorted out. If your service gets totally cut off in future, I'd advise always checking with customer services first if theres account issues to avoid this happening again.
Hope this helps