Problem with Old domain name redirect

I let an old domain name go when I registered a new domain name. Someone has recently registered the old name. I also installed the 301 permanent redirect so old posts would be redirect. I also paid for the domain name mapping which I thought would map everything to the new domain and therefore I did not need to keep the old domain name.

The problem is there are posts appearing on Google with the old domain name and post address and if you click on shown result it goes to a page with the old name which is just a parked page. This also applies to any posts i have done on other websites and comments on blogs.

I obviously have made a big mistake.

It there something I can do to ensure any pages appearing in Google are redirected to my current site as I have noticed a drop in traffic.

The old domain name was https://www.m4bmarketingblog.com and the cusrrent one is https://www.m4bmarketing.com.

Any help would be appreciated.

Susan