Believe it or not... 99% of text messages are trackable. If its phone to phone then they are usually stored forever in a central database that can be queried by law enforcement.
Tracking a www based message presents a significantly harder process. Tracking it back to the site is easy, if the site requires payment for the service or requires the user to log on then the task is much easier.
The problem is that there has to be sufficient reason to perform the tracking as court orders will be required to breach the data protection law that protect the "anonymous" user. Unless its a death threat or some other kind of serious abuse then I'm guessing you'll have to grin and bear it.
If its not serious but you consider it abuse then you should:
(1) Phone your mobile network provider and ask them to tell you where these calls are originating from. If they can tell you then they will.
If they can't tell you then tell them you are getting abusive txt messages from that source and they can go track it on your behalf. The result will probably be a block on that number to your phone.
(2) If you find out the name of the website then contact the web-admin or technical contacts from the RIPE records and explain to them that someone using their portal is sending un-solicited abusive txt emails. They may not tell you who it is but they can find out and stop it.
Not really sure if this is just a tracking of a valentine msg or stalker msg but if I can help then I will
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fug