Just a quick reply. The person you spoke to at your local Jobcentre Plus is wrong.
Being in receipt of DLA HRC exempts you from PCA so you don't need to complete an IB50.
This is the Statutory Instrument to quote
Statutory Instrument 1995 No. 311 The Social Security (Incapacity for Work) (General) Regulations 1995.
See section 10 which states:
10.—(1) A person shall be treated as incapable of work on any day on which any of the circumstances set out in paragraph (2) apply to him.
(2) The circumstances are—
(a) that he is in receipt of the highest rate care component of disability living allowance;
These regulations have not been repealed and still apply.
Call the JCP again and ask to speak to a supervisor and quote the Statutory Instrument given in the link.
Good luck.
Jim