is there any way to get my BTC back from the registration process?
In general there is no registration process for buying or mining bitcoin or for most types of bitcoin wallet. Certainly not in 2009.
I started mining march 2009, i remember registering.
There is no registration process for mining. At least not in the January 2009 Bitcoin software released by Satoshi Nakamoto.
At that time, I believe mining would have placed any mined coins into an address controlled by the private-key in a wallet on your PC.
Registering for a custodial wallet service (trading/exchange service)
There may have been a registration process if you had a "custodial" wallet, a type of wallet where you arranged with a third party for them to manage your wallet on your behalf. There are many such companies, all different. In that case you would have to contact the specific company that you registered with. This would not have been the case in March 2009 but maybe in later years you signed up with a custodial-wallet business to use their trading services? (In any case, this paragraph may be helpful to later searchers who find this question because they have the problem expressed in the title).
there are lists of dormant addresses, can they be used to get my BTC back?
No. To regain control of the BTC you need the private-key that was stored in the wallet. The address is not enough.
2Registration with whom? There is no admin for the bitcoin network, users are responsible for their own coins. In March 2009 there would not have been any mining pools, etc, to sign up with, I think at this point you will either have your old wallet.dat file, or not. Best of luck. – chytrik – 2018-11-28T22:16:53.663