Not sure if you will be able to claim against any potential mortgage PPI but a few of these cases are popping up now but you would have to evidence that what you were given was contrary to any advice that may have been issued with it at the time. With a bank it is normally offered on a "non advised" basis for a mortgage which means that you take it on your own choice and not advised to take it. if it is through broker then you are going to have to prove and evidence beyond the advice given how the product was "mis sold" to you. For the loan there is a good chance that you may have a claim as PPI is often just automatically added to the loan without choice and notice. It is this lack of advice and the automatic assumption by brokers/advisers/providers that people want these policies but with disregard to the many people that couldn't have claimed on this polies (but would have no doubt found this out if a property fact find had been done) why we have this situation in the first place.
The text message you received is almost certainly a spam text message sent out by a company to try and draw business, there are hundreds of them going around at the moment. While it is not likely that it is a scam message that you recieved it is quite likely that any company that advertsiees in this fashion has to make back the costs of sending out tens of thousands of text messages and the way they do this is to increase the percentage of what they will receive from your award. it is not unknown for companies to say that they will take 33% and then charge other fees on top of this so that their share soon becomes more than 75% of what is rewarded to you.
There is no reason why you cannot claim the PPI yourself, there are plenty of template letters on the interent and it will have the grand cost of £10.00 plus what ever postage may be involved.
If you have a genuine claim then screw the companies for every penny you deserve, but just don't go through a thrid party because it won't just be the policy providers that will get well and truly screwed.