The local authority has a duty to secure the special educational provision in section F of an EHC plan. Section 42 of the Children & Families Act 2014 contains the legal duty.
The first step will be to raise your concerns with the school. There may be reasons why support has been changed or delayed, which you are reassured about.
If you have discussed your views with the school and still have some concerns that provision in a plan is not being made, you should let the local authority know by contacting the SEND Service.
IPSEA have some useful guidance including an example letter, if you have been unable to resolve by contacting school/the local authority.
The SEND Code of Practice says:
When an EHC plan is maintained for a child or young person the local authority must secure the special educational provision specified in the plan (9.131)
The Clinical Commissioning Group (or other health commissioners) are responsible for arranging any health care provision specified in section G of the plan.
If the EHC plan specifies social care provision in section H1for a child under 18, the local authority will have a legal duty to make that social care provision under that Act (but not any other social care provision in section H2).
For a young person over 18, the care element of the plan may be provided by adult services under the Care Act 2014.