If you phoned BT (using a number which you trust) there can be no reason to worry.
If they phoned you when you expected them too then, again, you shouldn't have anything to worry about.
It's only unsolicited calls which can be dangerous.
It's common practice for a bona fide company to ask you to go online (and possibly to allow them access to your computer) if they think that it can help them solve your problems. I recently persuaded another ABer to phone the company which had supplied his new computer (which wasn't functioning properly). They took control of it over the internet (with his permission) and completely reinstalled Windows (thus solving his problem).
I doubt that you've got anything to worry about.