1 thing is that you can try what phoenix suggested.
Another is that you can try this method:
Make sure your modem is directly interfaced with the wall terminal without any use of long lengths of phone cable which degrades signal quality.
1. Unplug all phones that are on this ADSL line.
2. Plug only 1 phone with the splitter and the microfilter.
3. Try surfing.
4. If line drops then there is seriously something wrong with your line's stability, i had this issue before but now solved after Singtel upped my signal.
5. If line does not drop then slowly start adding your microfilters back 1 by 1.
Another point to note is that try not to exceed 3 microfilters on 1 ADSL line as this will likely cause the line to be unstable.