Hi, with regard to your post:
"If I am working again at age 74 and already collecting my age 70 SS benefits; 1. why are social security and medicare taxes being taken from my payroll? ------- This is because, like our federal/state/local income taxes, we pay the tax on our income, specifically, that income derived from our work efforts.
You are earning from work efforts, so you are subject to this tax, just as you are subject to your federal (and possibly state/local) tax on work income. It is a tax, so we all must pay it.
"It We already have a medicare deduction from our social security benefit. ------- Now that is NOT a tax. That is simply your insurance premium that you must pay if you want the insurance. Akin to employer provided medical insurance, who may pay part of our health insurance premiums as a work perk, as part of our compensation package (which means we really pay it), often we STILL have to pay more out of pocket through additional taking from our pay check to pay that monthly premium. Your medical coverage is partly paid for via government from those taxes of Medicare you paid in all these years, and partly through the 104.90 you pay out of your SS check. (And, this coming year, some other Medicare beneficiaries will be putting part of the bill for your Medicare, due to the hike in Medicare premium cost coming in 2016 - but that is a whole other matter.) But in any event, our FICA taxes are on thing all people pay, even if they aren't using Medicare, and premiums are further paid partially by beneficiaries like you who ARE buying the Medicare insurance.
"2. will my benefit increase at some point because I am paying in more? Thank you." ------- If your yearly income is higher than any prior yearly income in your top 35 years, then your calculated lifetime average monthly earnings will increase. Since your SS benefit is a % of your average monthly earnings, if that earnings figure increases, so will your Ss benefit (incrementally).