Living in Samut Sakhon then Thai Immigration in Samut Sakhon will assist you with extending your Thai visa while in the country. They will be able to extend a tourist visa and also extend a Thai marriage visa, Thai retirement visa or assist you with your 90 day reporting if you have already extended your visa in Thailand.
You can while in Samut Sakhon also apply for a re-entry permit if you are leaving Thailand and do not want to invalidate your Thai 12 month extended visa. You can also transfer a visa from an old passport to a new passport. The contact details are below.
Thai Immigration in Samut Sakhon
17 Moo3 Amphoe Mueang
Email: firstname.lastname@example.org / email@example.com