First question is what is the condition of the engine oil?
If it is good then:
Sounds like the transmission cooler inside the radiator has a breach.
Your mixing coolant and transmission fluid together.
Not a good thing for the transmission.
My suggestion is to stop driving it at once.
Pull the radiator and have it tested / repaired if possible if you have a local shop.
My guess is that it is of plastic construction so more than likely your going to need to replace it and completely flush out the cooling system thoroughly.
Next step ( providing the transmission hasn’t grenaded itself) would be to flush out ALL the contaminated fluid out of the transmission with fresh fluid.
Hopefully you can revive it.
The last thing would be to look into installing an external transmission cooler and bypass the one going through the radiator all together.
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