If it's advertisement then there must be some sort of internal leak of postpaid numbers in Globe. Someone who has access to view postpaid numbers may have benefited from leaking such private information to desperate advertisers.
It would be different case if the sender is sending personal sms as if he/she knew you. In that case your number must be a recycled one, meaning someone in the past may have used that postpaid number and his/her contacts are still texting it.
Your situation may be even safer as compare to my friend's postpaid globe number with all consumable plan. His monthly load is always being robbed by unknown subscription which he is not engaged with. When he called globe the CSR said they cannot do anything to stop it and only he can stop it thru certain procedure. He end up discontinuing his globe plan due to disappoinment.
These are just my opinion based on observation...
Poor globe it didn't get better. poor people we only have few choices for telco.