unless and until you have done something wrong to someone no amounts of BAD DUA can work on you. BAD DUA is like 'what goes around comes around"
I can think of black magic over here but again it’s a very sinful thing to do and I am certainly not in a position to judge if it’s black magic or not.
please take broken engagement as a positive thing only Allah knows what He has saved you from. A broken engagement is much better than broken marriage. No need to feel devastated about a broken engagement.
Read what people here have told you and please remove this fear from your heart the more fear you have more these things will affect you. Have a strong emaan. You will be able to fight everything then.