Contributary ESA entitlement before migration from irESA to U/C?

Hi, as part of the managed migration from irESA to U/C like others I've been told I'm eligible for New Style ESA.

When I questioned this on my journal I was told:

Universal Credit is only replacing Income-related ESA. As you were entitled to Contributory-based ESA as part of your ESA claim, that will continue being paid to you under the new name of New-style ESA

Which begs the question was I previously entitled to cESA as well as irESA? When I applied for ESA back in 2011 and at all reviews since then I have been only awarded irESA, so why wasn't I also awarded cESA when they now say I was entitled to it? Also, does this now mean I should apply for a retrospective MR regarding them not paying me cESA ?

Thanks,
Ali.