I always understood that the money you contribute is used to pay state pensions of those already retired thus when you retire other working people pay yours.
The money was never hypothecated (reserved to pay future costs). It is and always was just another tax that went into the treasury coffers.
What NI does do is build entitlement to things the state provides - like state pensions, "free" NHS services, unemployment benefit, lockdown payments etc. If the true cost of all these things were really covered by NI alone, your NI deduction would probably be 10 times higher than it is today.
And it's no use saying "I've paid in all my life etc.." Yes you may well have paid what you were supposed to, but unless you earn north of about £70K p/a on average throughout your working life then you are a net taker "scrounging" off those richer (and paying more tax) than you.