The Cable Communications Association said these were among a range of anti-competitive practices that hampered the industry and must be stamped out.
Richard Woollam, director-general of the CCA, said he was not accusing BT of any orchestrated campaign and that the problem was probably due to over-zealous employees.
The CCA first complained to the watchdog, Oftel, last year, and has raised the issue again within the past few weeks.
"We need to have a very fast response to these things. It cannot just drift on," he said.
A spokesman for BT said: "If there is any instance of such behaviour we would treat it as a serious disciplinary offence. There is no evidence of which I am aware."
Cable companies should take their concerns to BT or to Oftel, the spokesman added.
Mr Woollam also claimed that BT did not always give enough warning when introducing a price change.
"All these things add up. The small things are as bad as the big ones," he said.
The CCA has called for tougher competitive powers for Oftel, including the imposition of fines if BT is found to be acting in an anti-competitive way. A report by Oftel on the future of the industry, due out this summer, is expected to highlight the problems in regulating dominant companies because of the general weakness in UK competition law.
Mr Woollam said the cable industry would accept the removal of caps on BT's prices if wider competition powers were given to Oftel.
"If price caps are released it will be the beginning of real competition," he said.