i switched from prepaid to postpaid too...
1st i also having some problem to access into OCS for the 1st week and the data no up to date, still at prepaid although using postpaid... later on i access again after week without register anything, and everything back to normal and stated as postpaid...

i dont think the maybank TAC will be any issues between prepaid and postpaid, bank never have no idea what package that we using, they just send the TAC to particular number... if u can receive SMS from your friends,should no issues on your postpaid, u should inform this issues to maybank and digi bcos is their server no working fine with each others... if you cant even receive any sms, call digi and complain...

1. I oso face tis problem b4, i change from maxis to digi. Complain to digi customer service, they say need to wait 72 hours, ok...i wait for 3 day, still can't login, complain again, say wait another 24 hour, after about 6 days transfer from maxis to digi, i finally can register my OCS. Wait 5-6 days later and c how....
2. I oso facing same problem when request TAC from doing online banking, wonder when they will fix it, i request TAC yesterday, till now, no even one sms received...

TAC problem might because of bank server.. but so far, the TAC never failed to be sent on my celcom number. usually Maybank TAC is faster (less than 30sec) while Cimb TAC may need to wait up to 1 minutes..