The contractor has no contractual obligation to provide you with a quotation for a task order and you have no powers to issue an instruction for it to do so. The contractor therefore has no obligation to obey that instruction, see clause 27.3. As service manager you issue task orders that include a priced list of items (see clauses X19.1(2) and X19.2). You are required to ‘consult’ with the contractor before you issue a task order (X19.2), but that does not give you the power to instruct a quotation.
A defect is a defined term, see clause 11.2(4). Not obeying an instruction does not fall within that definition and therefore is not a defect.
It will often make sense for you to give the contractor the opportunity to produce a priced list of items for the task, but they are not obliged to and you cannot force them to. Instead you should issue the task order under clauses X19.1(1) and X19.2 with what you think the prices will be. The contractor is then be obliged to put your instruction into effect, again see clause 27.3. The contractor may be able to argue afterwards about the prices but, if you do not agree, the contractor will have to ask the adjudicator to sort it out.