You may be better off contacting NowTV live chat for account related matters.
I am assuming you only have one NowTV account and have tried your NowTV passes on a number of different playback devices (if you have more than one device).
Another long shot is to delete the NowTV App if your device allows it, download a fresh NowTV App, power down the device and once the device is rebooted, sign back into the NowTV App on the playback devices with the NowTV account login details that you paid the NowTV Pass on the 28th December.
I would also be inclined to try re adding your existing bank card details used on your NowTV online account once again, just in case this is blocking access to your Pass.
Here's the link page below to NowTV live chat (click on the green chat online button).
If the green chat online button doesn't work, try another internet browser or another device with a browser on it.
Should you still have no joy getting in touch with live chat, send them a message using the web form from the same link page below.