janway:i am on a spreading warmth tariff with npower
In that case my advice to use a comparison website doesn't apply. My apologies. Social tariffs don't feature because they are not universally available. The Scottish Power social tariff is called Fresh Start.
I'm not sure whether you made the Scottish Power sales agent aware that you were currently on a social tariff. I'm sure it's a very serious issue for a sales adviser not to deal with that issue sensitively. Hopefully that will come out in your complaint (assuming you made Scottish Power aware of that fact).
As to which tariff is best, that's very difficult to say. Social tariffs are not necessarily intrinsically cheaper but offer comparable prices regardless of payment method and other benefits.