scubawasp is correct, there is no requirement to contact anyone to enter a MATZ. Even if it is operational and manned you can enter without talking to anyone and they cannot refuse permission because you do not need permission. MATZ 24 is therefore just a guidance that you can speak with the MATZ controller at weekends as well as weekdays. Its probably sensible and courteous to speak with them but they can only offer guidance and traffic alerts as you do not need permission or radio contact to enter the MATZ.
Within most MATZ's there are usually airfields with ATZs and to enter these you need permission, very often this is refused because of traffic or security reasons. Also, if you cannot get permission then you canot enter the ATZ, so if they don't answer the radio you need to go round the ATZ
eg I do aerobatics within the Lakenheath/Mildenhall MATZ. I speak with them on the radio and tell them what I am doing and they give me traffic advisories. Once or twice they have asked if I can move a mile or so to be clear of their ILS but that has been a request which I would be perfectly within my rights to refuse... I have always moved so as to be helpful. They normally instruct all VFR pilots to keep away from the Lakenheath and Mildenhall ATZ, probably for secuity reasons as much as anything else. Sometimes there is no answer from the MATZ contoller and then I just do what I want but keep clear of the ATZs.