Guaranteed Minimum Pension (GMP) Question

Stonedrose_2

I'm actually writing on behalf of my dad and would appreciate any advice that can be given at all. I apologise in advance if I don't have all the information for an informed response!

My dad has a private pension that he has been drawing on since 2002 (age 58). During these last 8 yrs he has been receiving a supplementary pension alongside this pension to compensate for the fact he doesn't receive his State Pension until the age of 65. He has also been receiving his Guaranteed Minimum Pension - GMP - and this is (I believe) because he contracted out of the SERPS.
Understandably, things change once he reaches 65 - which was earlier this month.
He has a statement from his pension plan which states the following:

Adjustment at age 65

a) GMP increases estimated £860.60 are payable in addition.
b) The supplement, inclusive of annual reviews will cease.
c) State benefits will become payable in addition.

We were of the understanding that whilst the supplement would cease, the GMP would continue to run, as seems to be stated above. However, after repeated attempts at contacting the pension scheme, they told my dad that he should be in receipt of a letter outlining the new figures (he isn't) and that the GMP figure of £860.60 would cease also along with the supplement.

Does this sound right to anyone? It seems to us to contradict what has been stated by them previously, and additionally my mum has the same letter and she is in fact receiving her GMP of a whopping £75 per annum, but nevertheless she is fact receiving it, whereas my dad is being told he will not.
This is obviously causing untold stress but we really need to know one way or the other. If anyone can help in any way it would be most appreciated.
Thanks
Claire