I agree with James's comment. You can say either of these: I played well at one time. I used to play well. But there's no need to combine both in one sentence. If you do, it's not grammatically wrong, it's just repetitive. Here are some longer sentences, if you're interested. I played well at one time, but now I spend all my free time skydiving! I played well as a child, but when I was 12, my parents said the lessons were getting too expensive. I used to play well, but I don't practice much anymore. I used to play well, but I haven't touched a piano in 10 years. I used to play well, so when I resume lessons next week, I hope it will all come back to me quickly.

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The first is good. The second is not wrong but it is redundant; you can just write “I used to play well,” and “at one time” adds nothing to the meaning.