I think I have the answers to these last three clues but I don't know why.
16a Clobber with element of speech when confused. ?A?B?E? (Garbled)
20a Talking rubbish with more nasty dog. ???T?E?L?R (Rottweiler)
19d Two dots changing hands in Costa Rica? ???O? (Colon)
Anyone help? Thanks in advance.