I think that example almost works with either a comma or a semi-colon.
Semi-colons have (at least) two uses:
One: To combine two clauses that could each stand as a sentence on its own, without using a conjunction.
Sally saw the box. She opened it.
Two separate sentences.
Sally saw the box and she opened it.
Two clauses that could be separate sentences joined with a conjunction.
Sally saw the box; she opened it.
Two clauses that could be separate sentences joined with a semi-colon.
Your example almost fits this pattern. If you said "I presented" instead of simply "presented", then you would have two clauses that could each stand on their own. You are connecting them with a conjunction -- "and" -- so by this convention you would use a comma. You could omit the "and" and use a semi-colon instead.
Two: Semi-colons are used to separate elements in a list when the elements are themselves lists.
We have dresses in several color combinations: red, green, and blue and yellow and orange and black, pink, and white, and brown and tan.
The sentence is confusing. How many color combinations are there? Which colors go together?
With semi-colons we can at least give some hope of deciphering it:
We have dresses in several color combinations: red, green, and blue; yellow and orange; black, pink, and white; brown and tan.
Your example appears to fall in this category. You have two lists: things you attended and things you presented. The first element of the list is itself a list. So you can separate the two elements with a semi-colon.
In this case it's not really necessary, because the presence of two verbs -- attended and presented -- should make it clear where the two lists are separated.