Tenses, structure of a phrase, grammar

[Ludanata]

Hello. We are translating a very difficult Russian book into English and got stuck by one sentence which we can't shape grammatically. Will you, please help to do this.
They did smth. Then the situation changed. Still they continued to do that smth for a long time thereafter.

All actions are in the past. Instead of " continued" what tenses cand be used? The would do that for a long time thereafter? They had been doing that for a long time thereafter? They went on doing that for a long time thereafter?

Thank you in advance for your help!

Liudmila

[Alan]

'They went on (doing)' would accurately convey the required meaning!