If you have just a one-stage carbon filter, you have a very little chance of removing chloramines, which are much harder to remove than chlorine and it takes more carbon and longer contact time. I have a two-stage carbon filter, and the chloramines are still measurable at the RO output, and after two month, the chloramines removal rate drastically deteriorates (well before the carbon is fully exhausted).
Life of the RO membrane will be shorter because of chloramines, but as long as our water companies want our water to be safe, this is the price we have to pay.
If you can't measure chloramines at the RO output, that's because your source water doesn't have chloramines, not because your RO filter has removed it completely.