Where can kids take swimming lessons? (Barcelona)

I would like to sign our son (who is 7 years old) up for swimming classes after school and then during the summer. Could anyone recommend a good place near the Sarria/Les Tres Torres/San-Gervasi area?

Or is anyone on here a swimming instructor who has access to a swimming pool to give classes?

Everything seems to be very complicated here. We went to DIR Diagonal last year and we came back last week to be told that we needed to provide them a bank account to register for classes which we feel unnecessary (the rep would not take our cash but another mom just paid cash just fine. Why???). Bona Sports is also very bureaucratic because we are not members. Both places told us that someone would call to make "exceptions" but of course no one has called. Why taking swimming lessons here is such a convoluted event, I don't know.