From what I understand of your question, if the PM is (a) not following the contract in giving written instructions and (b) then playing silly buggers around what they said, then :
- you need to early warn in writing that until you receive the instruction to do something different, you have to contractually carry on as other wise (a) you would not be providing the works in accordance the contract (one of your main obligations under clause 20.1) and hence be in breach of contract and (b) the longer you carry on doing what is no longer wanted, the higher the costs to the Employer of taking out what you were doing and doing something different.
- you carry on doing what you were doing until your receive the email / piece of paper which instructs you to do something different. If the PM does not notify this as a CE and instruct a quotation, you then then notify.
- you need to early warn in writing that until you receive the instruction to do something different, you have to contractually carry on as other wise (a) you would not be providing the works in accordance the contract (one of your main obligations under clause 20.1) and hence be in breach of contract and (b) the longer you carry on doing what is no longer wanted, the higher the costs to the Employer of taking out what you were doing and doing something different.
- you carry on doing what you were doing until your receive the email / piece of paper which instructs you to do something different. If the PM does not notify this as a CE and instruct a quotation, you then then notify.