I'm not sure why you are seeking a rebate?
You chose not to use your webspace, as you say you had 'other webspace' available.
You have had free use of the service since March.
Presumably, it was your choice to use your mobile, rather than use the freephone or National Rate numbers from a landline in order to get your account details sorted out.
If you moved house in March, presumably they wrote to you at your previous address between March and now?
click here for contact methods / details for NTL, or see the back of the bills that they will presumably start sending you in the near future.