Again, if you paid via paypal and within some number of hours, you received texts on your phone that you say you never logged or registered anywhere with the details of your payment transactions to the store, then you indeed registered that number somewhere at some point in your history. There is absolutely 1) no way somebody was able to pull your old number out of the internet or phone provider ether in that time and 2) have the specific details of your order and 3) especially with no way to gain financially from the texts if it was intended as a scam.
I know you say otherwise, however, I am in the IT business, security and all, own my own online store, and also do ecommerce on a daily basis. I have experience in this area, and if anyone is going to get hacked, it would be me as my info is EVERYWHERE, with 3 phones in our family, 10 tablets, and about 400 registered sites with our info.
Be careful, yes, but it simply isn't worth spending any more time on this particular incident. You are not out anything, and the phone isn't a gateway to ruin your financial foundation. If you are that worried, smash the phone and sim card, and start with a new one. Delete your paypal account completely, and make a new one with a new email address. Done....
I don't want to sound harsh, but being less than educated on how scams work means you are potentially even a bigger target. You need to know how and why these things work, so that you can recognize the signs. This simply doesn't match any of the known patterns, and also isn't logical as you are calling the situation out. The more you research and listen to others, the better prepared you will be in the future. Things like "never fund your paypal from your bank, but always use a CC behind it with good protection" and "create different email addresses for different online access, like one just for friends and family, one for forums, and one (or more) for online purchases". Also another big one, "never use the same password twice on any site or email account". These 3 tips will save you grief in the future. These are my 3 Golden Internet Rules.