How to print an 18x24 poster with acrobat onto multiple A4 pages using a regular printer?

Greetings to everyone at the ICPO.

I am a hobbyist painter and i have this high res image that i have upscaled and make-overed to 18x24. 

This is confirmed by acrobat image properties.

I wish to print this image out with a regular printer that prints a maximum of A4 size (about 8x12). 

Printing services in my area don't print 18x24 and they don't do single paper only batch.

In short: I need to split up the image into multiple A4's. Acrobat automatically does this, but it does NOT let me select custom 18x24 size. For some reason, when i click print it shows ' 22x25.5' and 6 pages of A4.

I have printed this out, cut it and glued it together, but the size is wrong. 

I tried all options, including the 'poster' and 'multiple' etc settings, none of them give me option to set the print to 18x24. 

Don't bother sending me to printer settings, its a basic printer, has no special settings regarding posters.

So what gives? Why can't i select 18x24? Why isn't there an option in the first place? Why Acrobat is trying to print an 18x24 image into 22x25.5? Why is the option at ' pages to print' is greyed out?

For your answers, i thank thee in advance.