I find that very hard to believe because I also live in a property that is managed by Martin and Co, and had heating problems in December. The heating engineer called to my property within 24 hours of me reporting it even in about three feet of snow.

Just to let you know under law a landlord is legally bound to provide their tenants with both adequate heating, and an unrestricted access to a clean water supply (including hot water). These both being two essentials that no human being can live without.
If your heating breaks down or you have no heating in your rented property, then this is classed as an emergency repair/requirement and under law your landlord is legally bound to fix it within 72hours of it going out of use. The fact that you have gone 3 months without heating is not only shocking but criminal offence and if you reported it to an authority such as your local council or shelter, then your landlord/letting agent would be in major major major trouble!

http://england.shelter.org.uk/get_advice/renting_and_leasehold/rights_and_responsibilities

or

http://www.direct.gov.uk/en/HomeAndCommunity/Privaterenting/index.htm

Probably best to call them both and get advice over the phone.