The T&C of the cards are not ambiguous at all. They make it clear that only "participating" Marriott's accept them. If OP did not confirm with the specific property at which he was booking that it was a "participating" Marriott and it turns out that it is not, he has nothing to complain about here on FT, to Marriott or to the individual property.

It's regreatble for OP, but the T&C really do matter and here, where an individual property doesn't participate, it simply won't take them.

As to the entire issue of credit limit, what may be happening is that as OP is running up a bill, the property is upping the authorization.