The only problem is, my favorite promo only has 7 days validity and though there're that 15 days validity, but it is too expensive and it is the same price from other telecom with 30 or 28 days validity.

Yeah that's no mistake. The provider probably knows they're more reliable and therefore preferred, so it's a neat trick giving you a promo with a ton of data, but less time to enjoy it. Some even take it a notch up by throttling your speed when you reach a certain usage limit. Some tell their customers this and others just keep it on the low.

Good thing there's available Pork blood

Curious what you do with the blood