Twaddle.
We still have rules in English. It's not a free-for-all, with rules arbitrarily concocted by 'people' based on ignorance or laziness.
Yes, it's an evolving language, but to fabricate a notion that 'if people are saying it, it's correct' has no value.
Yes, I was taught it, and yes, I have seen it. And it is perfectly OK.
This has nothing to do with 'textspeak' (that, by its very nature, would mean people wouldn't punctuate it properly anyway), and everything to do with perfectly legitimate written English.
It's perfectly legitimate and acceptable to use double contractions.
Shouldn't've
We'd've
Ha'p'orth
Fo'c's'le has three contractions (though often shortened to two - fo'c'sle).