So, both eldritch godling and cleric are classes that "classes that grant both 0-level and 1stlevel spells at level 1" so you add their levels together for MiM, for a caster level of 3.
Mystic Theurge certainly isn't a class that "classes that grant both 0-level and 1st level spells at level 1." You could argue whether by RAW it's even a "class that grants up to 4th level spells," but it pretty clearly is, so you get *half* its levels, or in this case 5. Same with Arcane Heirophant, for 3. Your caster level is 11.... worse than a normal Mystic Theurge spell.
If you decided MT and AH counted as "classes that grant both 0-level and 1st level spells at level 1." you's still top out at CL 20 with that 20-level build.
What MiM is most useful for is a eldritch godling/cleric built without MT, or one with MT that wants a little extra CL, but the rules of MiM can never give you a CL that exceeds your character level.
Now, I admit, this may seem like a house of cards to you, but this is honestly how I took it the first time I read it.
If you go by this line of MT:
Spells per Day:...This essentially means that he adds the level of mystic theurge to the level of whatever other arcane spellcasting class and divine spellcasting class the character has, then determines spells per day, spells known, and caster level accordingly. ...Taking this literally, it might not be such a stretch to say that your effective level for CL calculations for Eldritch and Cleric is 19 and 18 respectively. Taking it to the next step:
To determine your caster level for all your spellcasting classes, add all your levels in classes that grant both 0-level and 1st level spells at level 1,
At this point I added 19 and 18 for 37.
(Ignoring the fact I don't see how you qualified for Mystic Theurge)
I use two feats, one from 3.5, Versatile Spellcaster (Races of the Dragon) and Heighten Spell Metamagic, which are legal methods of entering MT early according to WotC.
Anyway, I'm not trying to argue my way into a rule change ;-p, just clarifying where I am coming from.