Mastercare no service delivery for me

I find the service delivery with Mastercare to be extremely lacking. It is great that the technician comes out and that the problem is diagnosed but the long wait for parts is disadvantaging me as a paying customer. Surely they should deal with other suppliers so that the customer does not have to wait for weeks on end and yet they have to pay each month for these parts that have to be sourced from a supplier that is so inefficient.