I also received similar calls from 22990 periodically. I started a live chat with Celcom Representative (S) and this is what I (M) got:

S: We are unable to stop the call. You are advised to ignore or cancelled the call received.
M: if i ignore or cancel it, is there any charges for it?
S: No.
M: if i pick it up, charges incurred?
S: You'll be charged if you subscribe the CMT service only.
M: why there is this call periodically from 22990
M: it is annoying but unable to stop it?
S: Yes, I'm unable to block / stop the call from said number.
S: I apologies for inconvenience caused.

so just ignore or cancel the call will do =)