Membership renewel marketer. You or the previous owner of the number you have, most likely has some sort of membership (probably anual) and this company was hired on behalf of that organization to fetch renewels. There is an option to decline and remove your number from the list. Just call the number back and follow the instructions.
The Denver Botanic Garden reminding me to renew my yearly membership. I even got a discount; guess it pays off to not renew early.