It's important to reflect on our intention. The Buddha is recorded to have said, "Intention is Kamma". So if our intention was good, it creates good Kamma. If we were generous, but we lacked some wisdom, then we consider the blame and see whether we could learn from it. If, through investigating in this way, we realize that what we did was good, and the blame is undeserved then we can reflect that the person blaming us is "the owner of their own Kamma", and develop more Equanimity towards the blame. "Praise and Blame" are a pair of opposites that we meet throughout our life. Some people will blame good actions, but if we allow that blame to prevent us doing good actions then we don't develop good Kamma - which is our true refuge. So we need to reflect on the relationship between Kamma and intention.
Kamma, good actions bring good results. If we don't really believe that within ourselves, then we have to investigated in our own practice, to see the power of Generosity. When we had a feeling of Generosity arising in our mind, how did it feel? Did it feel good or did it feel bad? If we remember that it felt good, we had more happiness there, and when we remember our good actions we have happiness thereafter, so being generous is a source of richness.
The Buddha taught that Generosity is the source of wealth. We can see this when we feel generous, we feel we have a lot, we feel we are rich. So we see that brings more happiness to ourselves. Whether another person blames us or not can't take that away from us, i.e. can't take our riches away from us because we've already experienced it.
So reflecting on Kamma, looking at your intention and remembering that "Intention creates Kamma", helps us to have more Equanimity towards blame if it is undeserved. If it is deserved, we can learn from it and increase our wisdom. Perhaps we were generous, but not wise with our generosity, maybe giving to people in a way that only increase their unwise desires. Perhaps we can learn to be more discriminating in the future.