Since February my phone (Huawei Y7) lost voice connection while speaking, while it stays connected. During April I upgraded (Samsung A32) but the same problem stays. At last they swop my Phone, but the problem persist. I query MTN directly, but received

Since February my phone (Huawei Y7) lost voice connection while speaking, while it stays connected. During April I upgraded (Samsung A32) but the same problem stays. At last they swop my Phone, but the problem persist. I query MTN directly, but received only automated answers promising to react within 5 working days. The latter never happens. Gerhard