I Used to have a side project called N******* J**** C***s, I uploaded an old recording on the internet and was immediately given a cease and desist by a punk band called N***** C***.
So I politely told them I'd be continuing using the name, had been using it longer than them and it's different enough not to mix them up, so jog on,
They then tried to pretend, laughably to be a lawyer which I then tore them apart on and eventually they sodded off accepting that this happens.
The names have been changed to protect the innocent.
However, I think them not responding to you isn't on. They should at least discuss it with you.